Well: Ask Well: Walking vs. Elliptical Training

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Walking and ellipticaling (which, if it is a word, should not be) are similar in some respects and quite different in others.

According to a number of recent studies, elliptical training results in greater activation of muscles in the buttocks and thighs than walking does, and less activation of muscles in the calf. Elliptical training also places greater strain on the lower back than walking because of how the muscles fire, a consideration for people with back problems.

It also involves less weight bearing. According to a study published this month in The British Journal of Sports Medicine, walking causes 112 percent of someone's body weight to strike the ground with every step, while only 73 percent does in elliptical training. This slighter jarring is an advantage for people with sore joints, but less so for those who hope that exercise will improve bone health.

If, however, you wish to burn calories, walking and elliptical training seem indistinguishable. In an interesting 2010 study, college students were asked to complete two 15-minute sessions of exercise, one on a treadmill, the other on an elliptical machine. In both, they were instructed to maintain a pace that felt challenging but sustainable (the equivalent of a 4 or 5 on a 10-point scale of intensity). Throughout, the researchers monitored the volunteers' energy consumption and found that it was the same regardless of which machine they were using. Only the intensity mattered — and you control that measure.

If your brisk walk feels less tiring than a session on the elliptical machine, pick up the pace; or alternatively, dial up or down the resistance on the elliptical machine.

Do you have a health question? Submit your question to Ask Well.

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Well: A ‘Code Death’ for Dying Patients

Sadly, but with conviction, I recently removed breathing tubes from three patients in intensive care.

As an I.C.U. doctor, I am trained to save lives. Yet the reality is that some of my patients are beyond saving. And while I can use the tricks of my trade to keep their bodies going, many will never return to a quality of life that they, or anyone else, would be willing to accept.

I was trained to use highly sophisticated tools to rescue those even beyond the brink of death. But I was never trained how to unhook these tools. I never learned how to help my patients die. I committed the protocols of lifesaving to memory and get recertified every two years to handle a Code Blue, which alerts us to the need for immediate resuscitation. Yet a Code Blue is rarely successful. Very few patients ever leave the hospital afterward. Those that do rarely wake up again.

It has become clear to me in my years on this job that we need a Code Death.

Until the early 20th century, death was as natural a part of life as birth. It was expected, accepted and filled with ritual. No surprises, no denial, no panic. When its time came, the steps unfolded in a familiar pattern, everyone playing his part. The patients were kept clean and as comfortable as possible until they drew their last breath.

But in this age of technological wizardry, doctors have been taught that they must do everything possible to stave off death. We refuse to wait passively for a last breath, and instead pump air into dying bodies in our own ritual of life-prolongation. Like a midwife slapping life into a newborn baby, doctors now try to punch death out of a dying patient. There is neither acknowledgement of nor preparation for this vital existential moment, which arrives, often unexpected, always unaccepted, in a flurry of panicked activity and distress.

We physicians need to relearn the ancient art of dying. When planned for, death can be a peaceful, even transcendent experience. Just as a midwife devises a birth plan with her patient, one that prepares for the best and accommodates the worst, so we doctors must learn at least something about midwifing death.

For the modern doctor immersed in a culture of default lifesaving, there are two key elements to this skill. The first is acknowledgment that it is time to shift the course of care. The second is primarily technical.

For my three patients on breathing machines, I told their families the sad truth: their loved one had begun to die. There was the usual disbelief. "Can't you do a surgery to fix it?" they asked. "Haven't you seen a case like this where there was a miracle?"

I explained that at this point, the brains of their loved ones were so damaged that they would most likely never talk again, never eat again, never again hug or even recognize their families. I described how, if we continued breathing for them, they would almost definitely be dependent on others to wash, bathe and feed them, how their bodies would develop infection after infection, succumbing eventually while still on life support.

I have yet to meet a family that would choose this existence for their loved one. And so, in each case, the decision was made to take out the tubes.

Now comes the technical part. For each of the three dying patients, I prepped my team for a Code Death. I assigned the resident to manage the airway, and the intern to administer whatever medications might be needed to treat shortness of breath. The medical student collected chairs and Kleenex for the family.

I assigned myself the families. Like a Lamaze coach, I explained what death would look like, preparing them for any possible twist or turn of physiology, any potential movements or sounds from the patient, so that there would be no surprises.

Families were asked to wait outside the room while we prepared to remove the breathing tubes. The nurses cleaned the patients' faces with warm, wet cloths, removing the I.C.U. soot of the previous days. The patients' hair was smoothed back, their gowns tucked beneath the sheets, and catheters stowed neatly out of sight.

Then, the respiratory therapist cut the ties that secured the breathing tube around the patients' neck. As soon as the tubes were removed and airways suctioned, families were invited back into the room. The chairs had been pulled up next to the bed for them and we fell back into an inconspicuous outer circle to provide whatever medical support might be needed.

I stood in the back of the room, using hand motions and quietly mouthing one-word instructions to my team as the scene unfolded — another shot of morphine when breathing worsened, a quick insertion of the suction catheter to clear secretions. We worked like the well-oiled machine of any Code Blue team.

Of those three Code Death patients, one died in the I.C.U. within an hour of the breathing tube's removal. Another lived for several more days in the hospital, symptoms under watch and carefully managed. The third went home on hospice care and died there peacefully the next week, surrounded by family and friends.

I would argue that a well-run Code Death is no less important than a Code Blue. It should become a protocol, aggressive and efficient. We need to teach it, practice it, and certify doctors every two years for it. Because helping patients die takes as much technique and expertise as saving lives.

Jessica Nutik Zitter is an attending physician at Alameda County Medical Center in Oakland, Calif. She is board-certified in both critical-care and palliative-care medicine.

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Well: Hospitals Safer Than Homes for Births

A new analysis suggests that giving birth in a hospital is considerably safer than having a baby at home or in a birthing center.

Researchers analyzed data collected by the Centers for Disease Control and Prevention from 2006 to 2009 on almost 14 million births, including 130,000 non-hospital deliveries. Their results appear online in The American Journal of Obstetrics & Gynecology.

They examined both early death (within seven days of birth) and neonatal death (within 28 days) among singleton full-term babies without congenital malformations. No matter how they parsed the numbers, babies born outside hospitals had higher rates of death.

Over all, babies delivered by midwives at home had nearly four times the risk for death compared with those delivered by hospital-based midwives, with the risk highest if the birth was the woman's first. With 25,000 home births per year in the United States, this means about 23 additional neonatal deaths annually.

Babies delivered by midwives in freestanding birthing centers had more than twice the risk for death compared with those delivered by midwives in hospitals.

Compared with midwife-attended births in hospitals, doctor-attended births had higher mortality, almost certainly because the most complicated births are generally handled by physicians.

When a birth was handled by others — policemen, taxi drivers and so on — the death rate was four times that of hospital births.

The researchers write that these results almost certainly underestimate the actual neonatal death rates in home and birthing center deliveries, because infants with complications are often transferred to hospitals, and the C.D.C. counts any subsequent death as a hospital outcome.

The lead author, Dr. Amos Grünebaum, a professor of obstetrics and gynecology at Weill Cornell Medical College, strongly discourages giving birth at home.

"We need to make hospitals provide some of the amenities you have at home," he said. "We need to make hospitals more like homes instead of making homes more like hospitals."

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Well: Circumcision Benefits Outweigh Risks, Study Reports

A review of studies has found that the health benefits of infant male circumcision vastly outweigh the risks involved in the procedure.

But the study, published online in Mayo Clinic Proceedings, also found that while the prevalence of circumcision among American men ages 14 to 59 increased to 81 percent from 79 percent over the past decade, the rate of newborn circumcision has declined by 6 percentage points, to 77 percent, since the 1960s.

The authors conclude that the benefits — among them reduced risks of urinary tract infection, prostate cancer, sexually transmitted diseases and, in female partners, cervical cancer — outweigh the risks of local infection or bleeding. Several studies, including two randomized clinical trials, found no long-term adverse effects of circumcision on sexual performance or pleasure.

One cost-benefit analysis that considered infant urinary tract infections and sexually transmitted diseases found that if circumcision rates were decreased to the 10 percent typical in European countries, the additional direct medical costs over 10 years of births would be more than $4.4 billion.

"Male circumcision is in principle equivalent to childhood vaccination," said the lead author, Brian J. Morris, emeritus professor of medical sciences at the University of Sydney. "Just as there are opponents of vaccination, there are opponents of circumcision. But their arguments are emotional and unscientific, and should be disregarded."

A version of this article appears in print on 04/08/2014, on page D6 of the NewYork edition with the headline: Childhood: Benefits From Circumcision.

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Well: Are You Programmed to Enjoy Exercise?

Phys Ed

Gretchen Reynolds on the science of fitness.

It's possible that some of us are born not to run. According to an eye-opening new genetics study of lab rats, published in The Journal of Physiology, the motivation to exercise — or not — may be at least partly inherited.

For years, scientists have been bedeviled by the question of why so few people regularly exercise when we know that we should. There are obvious reasons, including poor health and jammed schedules. But researchers have begun to speculate that genetics might also play a role, as some recent experiments suggest. In one, published last year, sets of fraternal and identical adult twins wore activity monitors to track their movements. The results indicated that the twins were more alike in their exercise habits than a shared upbringing alone would explain. Their willingness to work out or sit all day depended to a large extent on genetics, the researchers concluded.

But which genes might be involved and how any differences in the activity of those genes might play out inside the body were mysteries. So scientists at the University of Missouri recently decided to delve into those issues by creating their own avid- or anti-exercising animals.

They accomplished this task by inter-breeding normal rats that had voluntarily run on wheels in the lab. The male rats that had run the most were bred with the female rats that also had run the most; those that had run the least were likewise mated. This scheme continued through many generations, until the scientists had two distinct groups of rats, some of which would willingly spend hours on running wheels, while the others would skitter on them only briefly, if at all.

In their first experiments with these rats, the researchers found some intriguing differences in the activity of certain genes in their brains. In normal circumstances, these genes create proteins that tell young cells to grow up and join the working world. But if the genes don't function normally, the cells don't receive the necessary chemical messages and remain in a prolonged, feckless cellular adolescence. Such immature cells cannot join the neural network and don't contribute to healthy brain function.

In general, these genes worked normally in the brains of the rats bred to run. But their expression was quite different in the non-runners' brains, particularly in a portion of the brain called the nucleus accumbens, which is involved in reward processing. In humans and many animals, the nucleus accumbens lights up when we engage in activities that we enjoy and seek out.

Presumably as a result, when the scientists closely examined the brains of the two types of rats, they found that by young adulthood the animals bred to run had more mature neurons in the nucleus accumbus than did the non-runners, even if neither group had actually done much running. In practical terms, that finding would seem to indicate that the brains of pups born to the running line are innately primed to find running rewarding; all those mature neurons in the reward center of the brain could be expected to fire robustly in response to exercise.

Conversely, the rats from the reluctant-running line, with their skimpier complement of mature neurons, would presumably have a weaker innate motivation to move.

Those results would be disheartening, except that in the final portion of the experiment the scientists had reluctant runners exercise by setting them on running wheels, while also providing some born-to-run animals with wheels. After six days, the unwilling runners had accumulated far less mileage, about 3.5 kilometers (two miles) per rat, compared to almost 34 kilometers each by the enthusiasts.

But the halfhearted runners' brains were changing. Compared to others in their family line that had remained sedentary, they now showed more mature neurons in their nucleus accumbens. That part of their brain remained less well developed than among the naturally avid rat runners, but they were responding to exercise in ways that would seem likely to make it more rewarding.

What, if anything, these findings mean for people is "impossible to know at this point," said Frank Booth, a professor of biomedical sciences at the University of Missouri who oversaw the study. Rat brains are not human brains, and rat motivations are at best opaque.

Even so, Dr. Booth said, his group's data would seem to suggest "that humans may have genes for motivation to exercise and other genes for motivation to sit on the couch," and over generations, one set of these genes could begin to predominate within a family. But predispositions are never dictatorial.

"People can decide to exercise," whatever their inheritance, Dr. Booth said, and, as his study's final experiment suggests, they could rewire their brains so that moving becomes a pleasure.

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Well: Circumcision Benefits Outweigh Risks, Study Reports

A review of studies has found that the health benefits of infant male circumcision vastly outweigh the risks involved in the procedure.

But the study, published online in Mayo Clinic Proceedings, also found that while the prevalence of circumcision among American men ages 14 to 59 increased to 81 percent from 79 percent over the past decade, the rate of newborn circumcision has declined by 6 percentage points, to 77 percent, since the 1960s.

The authors conclude that the benefits — among them reduced risks of urinary tract infection, prostate cancer, sexually transmitted diseases and, in female partners, cervical cancer — outweigh the risks of local infection or bleeding. Several studies, including two randomized clinical trials, found no long-term adverse effects of circumcision on sexual performance or pleasure.

One cost-benefit analysis that considered infant urinary tract infections and sexually transmitted diseases found that if circumcision rates were decreased to the 10 percent typical in European countries, the additional direct medical costs over 10 years of births would be more than $4.4 billion.

"Male circumcision is in principle equivalent to childhood vaccination," said the lead author, Brian J. Morris, emeritus professor of medical sciences at the University of Sydney. "Just as there are opponents of vaccination, there are opponents of circumcision. But their arguments are emotional and unscientific, and should be disregarded."

A version of this article appears in print on 04/08/2014, on page D6 of the NewYork edition with the headline: Childhood: Benefits From Circumcision.

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Well: Panel Urges Low-Dose Aspirin to Reduce Pre-eclampsia Risk

Pregnant women should take low-dose aspirin daily to reduce their chance of developing pre-eclampsia if they are at high risk for the life-threatening disorder, an influential government panel said on Monday.

The United States Preventive Services Task Force's draft recommendation follows a growing scientific consensus that low doses may be beneficial to some high-risk women and their offspring. Low-dose aspirin reduced the risk of pre-eclampsia by 24 percent in clinical trials, according to a systematic review underpinning the new recommendation, which was published in Annals of Internal Medicine.

Low-dose aspirin also reduced the risk of premature birth by 14 percent and of intrauterine growth restriction — a condition in which the fetus doesn't grow as fast as expected — by 20 percent.

"For every four women who would have gotten pre-eclampsia, one case is prevented," said Dr. Ira M. Bernstein, the chair of department of obstetrics, gynecology and reproductive sciences at the University of Vermont. "The ability to prevent a quarter of disease is substantial."

Pre-eclampsia is a condition usually occurring in the second half of pregnancy and characterized by high blood pressure, protein in the urine, liver disease and blood-clotting abnormalities.

It is a leading complication for expectant mothers and their infants, affecting roughly 4 percent of pregnancies nationwide. The only "cure" is delivery. When a pregnant women develops pre-eclampsia in the second trimester, her infant often must be delivered prematurely to avoid severe maternal complications, like stroke.

The task force recommended that women at high risk for pre-eclampsia take 81 milligrams of low-dose aspirin daily after 12 weeks of gestation. High-risk women include those who have had pre-eclampsia in a prior pregnancy, especially those who have had to deliver preterm; women carrying multiple fetuses; and women who had diabetes or high blood pressure at conception.

But the task force also advised that expectant women with multiple moderate-risk factors "may also benefit from low-dose aspirin." These risks include obesity, a family history of pre-eclampsia, women older than 35, and African-American women.

A single high-risk factor merits low-dose aspirin use, but "it's a judgment call between physicians and patients as to whether a combination of moderate-risk factors is enough to justify taking low-dose aspirin," said Dr. Michael L. LeFevre, the chair of the task force and a professor of family medicine at the University of Missouri in Columbia.

Low-dose aspirin appears to cause no short-term harm during pregnancy, according to the new review of 19 clinical trials and two observational studies. However, potential rare or long-term harms could not be ruled out.

The largest trial followed infants 18 months after birth, and "found no differences in development outcomes," said Jillian T. Henderson, the lead author of the review and an investigator at Kaiser Permanente Center for Health Research in Portland, Ore.

The researchers also found that use of low-dose aspirin doesn't increase the risk of excessive bleeding after delivery, placental abruption (when the placenta detaches from the uterus before it should) or bleeding inside the baby's cranial vault.

Dr. Phyllis August, a professor of medicine in obstetrics and gynecology at Weill Cornell Medical College, praised the careful appraisal of the potential risks of taking aspirin. "They critically reviewed the risks, and well," said Dr. August, who for 20 years has had selected high-risk patients use low-dose aspirin.

In recent months, medical organizations like the American College of Obstetricians and Gynecologists and the American Heart Association also have advised that high-risk women use low-dose aspirin, with slight variations in who qualifies.

Still, "our general impression is it's being used infrequently," said Dr. LeFevre.

It's not currently possible to predict which women will develop pre-eclampsia or its complications. Some women classified as low risk still get the syndrome out of the blue. Effective prevention of pre-eclampsia has been difficult to pinpoint, experts said, but a remedy that could prevent a quarter of the cases is a significant step forward.

"We'd like to be able to prevent four out of four cases, obviously," Dr. Bernstein said. "There's still a lot to learn about why the other three are still getting it, and how to prevent their disease."

A version of this article appears in print on 04/08/2014, on page A14 of the NewYork edition with the headline: Aspirin Urged to Ward Off Pre-eclampsia.

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Ask Well: Ankle Replacements

Q

I understand that because of the number of bones and complexity of the other interacting parts, ankles aren't easy to repair back to their original condition, but how about just a ball socket replacement?

A

"We can and do" replace ankles, said Dr. Steven Weinfeld, an orthopedic surgeon and chief of the foot and ankle service at the Icahn School of Medicine at Mount Sinai in New York City. While not nearly as common as surgeries to replace a worn-out hip or knee, ankle replacement is on the rise, with as many 25,000 replacements likely to be performed this year in the United States, according to estimates from the American Academy of Orthopedic Surgeons. Like hip and knee replacements, the procedure treats debilitating bone-on-bone arthritis.

Until recently, though, the preferred surgical treatment for severely arthritic ankles had been a procedure called ankle fusion, in which rods are inserted into the ankle bones, fusing them and preventing them from grinding together. Ankle fusion generally eliminates arthritis pain, Dr. Weinfeld said, but it also warps how someone moves and can increase stress on knees and other leg joints.

So, for many people, ankle replacement is a better option, he said, although it too affects gait, at least at first. "The way people walk often changes when they have arthritis" in their ankles, he pointed out. They begin to hobble, and after surgery, "have to learn to walk normally again, which can be surprisingly difficult sometimes."

A more lingering concern is that today's ankle replacement devices are projected to last only 20 years or so, he said, meaning that a 40-year-old might require multiple replacements of the device during his or her lifetime. For younger patients, Dr. Weinfeld urges physical therapy, bracing, painkillers or other nonsurgical options first. But if your ankles twinge and creak, he said, consult a sports medicine specialist or orthopedist about what would work best for your situation.

Do you have a health question? Submit your question to Ask Well.

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This post has been revised to reflect the following correction:

Correction: April 7, 2014

An earlier version of this article identified incorrectly a source of statistics about ankle replacement. It is the American Academy of Orthopedic Surgeons, not Orthopedic Surgery.

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Well: Life With a Dog: You Meet People

Personal Health

Jane Brody on health and aging.

As I approached four years as a widow, the loneliness of a one-person household began to drag me down. Acquiring a four-legged companion, rather than a two-legged one, appealed to me.

And so, in February, I adopted a 5-month-old puppy, a hypoallergenic Havanese small enough for me to pick up and carry, even into my ninth decade, when I travel to visit family and friends.

While most dog owners I know encouraged my decision, several dogless friends thought I had lost my mind. How, with all my work, travels and cultural events, was I going to manage the care of a dog?

No one asked this when I decided to have children. In fact, few people consider in advance how children will fit into their lives. If you want a child badly enough, you make it work.

I am now making it work with Max II, little mischief that he is, and I am besotted. He's smart — smart enough to know when I really must work and cannot spend time throwing a ball for him. As I write this, he's asleep on the floor at my side, although during a phone interview two weeks ago, he managed to shred every piece of paper he could grab in my study.

Yes, he's a lot of work, at least at this age. But like a small child, Max makes me laugh many times a day. That's not unusual, apparently: In a study of 95 people who kept "laughter logs," those who owned dogs laughed more often than cat owners and people who owned neither.

When I speak to Max, he looks at me lovingly and seems to understand what I'm saying. When I open his crate each morning, he greets me with unbounded enthusiasm.Likewise when I return from a walk or swim, a day at the office, or an evening at the theater.

But perhaps the most interesting (and unpremeditated) benefit has been the scores of people I've met on the street, both with and without dogs, who stop to admire him and talk to me. Max has definitely increased my interpersonal contacts and enhanced my social life. People often thank me for letting them pet my dog. Max, in turn, showers them with affection.

Prompted by my son, a fellow dog lover, to explore the health benefits of pet ownership, I dug into the literature, focusing first on what pets can do for older adults, then branching out to people in all age brackets.

More American households have dogs than any other type of nonhuman companion. Studies of the health ramifications have strongly suggested that pets, particularly dogs, can foster cardiovascular health, resistance to stress, social connectivity and enhanced longevity.

The researcher Erika Friedmann, whose groundbreaking study in 1980 showed that, other factors being equal, people with pets were more likely to be alive a year after discharge from a coronary care unit, said studies also have linked pet ownership to lower blood pressure, cholesterol and triglycerides — even though owners drank more alcohol, ate more meat and weighed more than those without pets. Other studies have found that older people who walk dogs are more likely than those who walk with human companions to engage in regular exercise and be physically fit.

Controlled studies by Dr. Friedmann, a professor at the University of Maryland School of Nursing, have also demonstrated a lower level of physiological arousal from stress-inducing situations when a friendly animal was present.

I can't yet say that Max II has reduced my anxiety. I remain ever alert to his need to head outside and his attempts to chew or tear up anything he can reach. But there is no question that I am thrilled by his antics, endearing personality, unconditional love (even when I yell no), and the many connections he's fostered with both acquaintances and strangers.

As a study published in 2007 in Society & Animals concluded, pets "ameliorate some determinants of mental health such as loneliness." In a survey of 339 residents of Western Australia, the researchers found pet ownership to be associated "with social interactions, favor exchanges, civic engagement, perceptions of neighborhood friendliness and sense of community."

Elderly dog owners report "significantly less dissatisfaction with their social, physical and emotional states," according to a 1993 study by veterinary researchers at the University of California, Davis.

Children, too, can benefit from pet ownership, medically and socially. Rates of asthma and eczema are lower among children with dogs at home from infancy onward. Among boys in particular, who may have few activities that foster nurturing behavior, caring for a pet enhances emotional development and security, according to Gail F. Melson, professor of developmental studies at Purdue University.

She found that 5-year-olds who turn to pets for support are rated by parents as less anxious and withdrawn than comparable children who have pets they don't rely on.

But before acquiring any pet, and especially a dog, Alan M. Beck, who heads the Center for the Human-Animal Bond at Purdue, urges people to carefully consider the implications. "Look for an animal of an appropriate breed, size and temperament for your household," he said. "Do you have the income, exercise ability and time the pet needs?" In an interview, Dr. Beck suggested speaking to owners with the kind of pet you are considering. If possible, visit a household with one. Better still, he said, try pet-sitting for a few days or fostering an animal for a few weeks to appreciate more fully what pet ownership entails and to determine if you are up to the task.

"If you're going to get a dog, you should be prepared to spend time on basic training and socializing the animal," Dr. Beck said. "A properly socialized dog is better behaved and less likely to be aggressive and bite someone."

In an interview, Dr. Friedmann emphasized that "pets are not a panacea" to be treated like a drug taken when you feel unwell.

"Living with a companion animal involves responsibilities, the establishment of structured routines for feeding, exercising and nurturing," she said. "The benefits you derive from the animal are linked to these responsibilities."

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Well: Low Vitamin D Levels Linked to Disease in Two Big Studies

People with low vitamin D levels are more likely to die from cancer and heart disease and to suffer from other illnesses, scientists reported in two large studies published on Tuesday.

The new research suggests strongly that blood levels of vitamin D are a good barometer of overall health. But it does not resolve the question of whether low levels are a cause of disease or simply an indicator of behaviors that contribute to poor health, like a sedentary lifestyle, smoking and a diet heavy in processed and unhealthful foods.

Nicknamed the sunshine nutrient, vitamin D is produced in the body when the skin is exposed to sunlight. It can be obtained from a small assortment of foods, including fish, eggs, fortified dairy products and organ meats. And blood levels of it can be lowered by smoking, obesity and inflammation.

Vitamin D helps the body absorb calcium and is an important part of the immune system. Receptors for the vitamin and related enzymes are found throughout cells and tissues of the body, suggesting it may be vital to many physiological functions, said Dr. Oscar H. Franco, a professor of preventive medicine at Erasmus Medical Center in the Netherlands and an author of one of the new studies, which appeared in the journal BMJ.

"It has effects at the genetic level, and it affects cardiovascular health and bone health," he said. "There are different hypotheses for the factors that vitamin D regulates, from genes to inflammation. That's the reason vitamin D seems so promising."

The two studies were meta-analyses that included data on more than a million people. They included observational findings on the relationship between disease and blood levels of vitamin D. The researchers also reviewed evidence from randomized controlled trials — the gold standard in scientific research — that assessed whether taking vitamin D daily was beneficial.

Dr. Franco and his co-authors — a team of scientists at Harvard, Oxford and other universities — found persuasive evidence that vitamin D protects against major diseases. Adults with lower levels of the vitamin in their systems had a 35 percent increased risk of death from heart disease, 14 percent greater likelihood of death from cancer, and a greater mortality risk overall.

When the researchers looked at supplement use, they found no benefit to taking one form of the vitamin, D2. But middle-aged and older adults who took another form, vitamin D3 — which is the type found in fish and dairy products and produced in response to sunlight — had an 11 percent reduction in mortality from all causes, compared to adults who did not. In the United States and Europe, it is estimated that more than two-thirds of the population is deficient in vitamin D. In their paper, Dr. Franco and his colleagues calculated that roughly 13 percent of all deaths in the United States, and 9 percent in Europe, could be attributed to low vitamin D levels.

"We are talking about a large part of the population being affected by this," he said. "Vitamin D could be a good route to prevent mortality from cardiovascular disease and other causes of mortality."

In the second study, also published in BMJ, a team of researchers at Stanford and several universities in Europe presented a more nuanced view of vitamin D.

They concluded there was "suggestive evidence" that high vitamin D levels protect against diabetes, stroke, hypertension and a host of other illnesses. But they also said there was no "highly convincing" evidence that vitamin D pills affected any of the outcomes they examined.

"Based on what we found, we cannot recommend widespread supplementation," said Evropi Theodoratou, an author of the study and research fellow at the Center for Population Health Sciences at the University of Edinburgh. The second study also looked at bone health. While Vitamin D had long been believed to help prevent osteoporosis fractures from falls,

clinical trials in recent years have challenged the idea. The study also found no evidence to support that assumption.

"Vitamin D might not be as essential as previously thought in maintaining bone mineral density," Dr. Theodoratou and her colleagues wrote.

Dr. Theodoratou was not alone in suggesting people hold off on taking vitamin D supplements for now. Even though Dr. Franco found them to be beneficial, he said that more research was needed to show what levels are best. Instead of taking pills, people could improve their vitamin D levels with an adequate diet and 30 minutes of sunlight twice a week, he said.

"The most important factors in obtaining vitamin D are going out and doing some exercise and following a healthy diet," he added.

And in an editorial that accompanied the studies in BMJ, Paul Welsh and Dr. Naveed Sattar of the British Heart Foundation's Glasgow Cardiovascular Research Center pointed out that previous research "extolled the virtues of antioxidant vitamins only for major trials of vitamins E and C and beta carotene to show null, or even some harmful, effects of supplementation."

They said vitamin D pills should not be recommended widely until clinical trials that are underway shed more light on the benefits and potential side effects.

But Duffy MacKay, a spokesman for the Council for Responsible Nutrition, a supplement industry trade group, said that vitamin D is not easily obtained through food alone, and noted that exposure to sunlight has its dangers.

He said he agreed with Dr. Franco that more research was needed to identify "an optimal dose and duration" of vitamin D.

"But there is enough positive research currently to indicate that people should be supplementing with vitamin D for a variety of positive health outcomes," he added.

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This post has been revised to reflect the following correction:

Correction: April 5, 2014

An earlier version of this article incorrectly listed kale as a source of vitamin D. It is not.

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