Put 10 doctors in a room, goes the old joke, and you’ll get 10 different opinions. Unfortunately, that has become the story with vitamin D — and it’s no laughing matter. All the conflicting advice about how much to take has left many of us unsure of what to do.
The stakes are high. Inadequate vitamin D levels can increase your risk of dozens of serious health problems, including cancer, heart disease, osteoporosis, asthma, Alzheimer’s disease, and even the common cold and influenza. And apparently, nearly all of us are at risk of vitamin D deficiency.
Adit Ginde, MD, MPH, of the University of Colorado Denver School of Medicine, found that nearly three of every four Americans have either deficiencies or borderline deficiencies of the vitamin. But some experts contend the situation is far worse. “Ninety-five percent of Americans are deficient in vitamin D — that’s how big the problem is,” says John J. Cannell, MD, who heads the nonprofit Vitamin D Council. “It’s very difficult to overstate the seriousness of the situation.”
The main reason most of us lack adequate vitamin D is that we aren’t soaking up enough sun. When the sun’s ultraviolet (UV) rays strike the skin, they stimulate our bodies’ production of vitamin D. These days, though, warned about the risk of skin cancer, many of us don sunscreen whenever we go outside, inhibiting vitamin D production. And we don’t go outside nearly as much as we used to.
“Society has changed, and a lot of these changes have pushed us indoors,” says Robert P. Heaney, MD, of Creighton University in Omaha. “Our parents and grandparents spent significant amounts of time working or doing other activities outdoors. Until recently, children spent a lot of time playing outside. All of this enabled people to build up enough vitamin D reserves for wintertime, when it’s nearly impossible to make vitamin D in most parts of the country. Now, though, people go from homes to their cars to their work, and spend very little time exposed to sunlight. Computers, PlayStations and other electronics, along with 500 television channels, keep us occupied indoors,” he says.
Other changes have occurred as well: “In the 1930s, vitamin D was considered a miracle vitamin,” explains Michael F. Holick, MD, PhD, of the Boston Medical Center. That’s because researchers had just discovered that the vitamin prevented rickets, a near-epidemic bone-deforming disease among children in industrialized northern states and northern Europe. Dozens of foods were fortified with vitamin D, even hotdogs and beer. Then, in Great Britain during the 1950s, doctors started seeing cases of high blood calcium in young children that they mistakenly thought was due to overfortification of milk with vitamin D. As a result, doctors became wary of vitamin D, and Britain and most other European countries banned vitamin D fortification of foods.
Fast forward to the 1980s. That’s when doctors in India treated six tuberculosis patients with 3,800 international units (IU) of vitamin D daily for three months. The patients developed dangerously high blood levels of calcium. The doctors blamed the vitamin D, but they never measured the patients’ blood levels of the vitamin, or acknowledged that super-high calcium levels could be common in people with tuberculosis. That study added to the stigma, and five years later, based on the available evidence, the U.S. government warned that as little as 1,000 IU of vitamin D daily could be toxic.
All this shaped doctors’ feelings about vitamin D for years to come — and set the stage for today’s controversy about how much of the vitamin to take.
The tide of opinion started to change in 1999, when Reinhold Vieth, PhD, a University of Toronto researcher, questioned the Indian study. Writing in the American Journal of Clinical Nutrition, Vieth noted that up to 10,000 IU of vitamin D daily appeared to be safe. Indeed, that’s approximately how much vitamin D a person in a bathing suit, sans sunscreen, would make after spending 15 minutes in the summer sun.
Then, in 2004, there emerged a new wave of vitamin D research that continues today. Leading experts, including Cannell, Heaney and Holick, were recommending that adults routinely take at least 1,000 to 2,000 IU — and maybe even up to 5,000 IU — daily of vitamin D in specific circumstances. These recommendations were getting wide coverage in medical journals, magazines and newspapers, and vitamin D was again enjoying a renaissance.
But at the end of 2010, the federal government’s Institute of Medicine (IOM) issued more cautious recommendations. Although the IOM increased the recommended amount of vitamin D for most adults from 200 to 600 IU (up to 800 IU for those 71 and older), it also stated that most Americans have adequate vitamin D levels and that there was no need to take more than 600 IU of vitamin D daily to maintain healthy bones.
In our headline-driven world, this became big news, but the fact that the report focused on bone health was often lost. The IOM report did not address, in any substantial way, that larger amounts of vitamin D appeared to reduce the risk of infection, cancer and other diseases. Instead, the IOM noted that insufficient research prohibited recommending vitamin D to help prevent these diseases.
A firestorm of criticism ensued, mostly in medical journals and blogs, much of it coming from doctors who had anticipated the IOM would recommend larger amounts.
“The IOM report made absolutely no sense at all,” says Cannell. “If you take the report at face value, a baby and a 300-pound football lineman both need only 600 IU of vitamin D daily.”
The other view: “The IOM committee did its work without any preconceptions. It’s the data — the totality of data — that led to the numbers,” says Catharine Ross, PhD, a professor of nutrition at Pennsylvania State University, and the chair of the IOM committee. “The RDAs are for the general population, and from all the studies to date, there isn’t support for values higher than those that the report specifies.”
Cannell contends that the IOM report was filled with contradictions. “The IOM report acknowledged that people could safely take up to 4,000 IU of vitamin D daily. This amount of vitamin D will boost blood levels of vitamin D to 40 ng/ml (nanograms per milliliter of blood), but the IOM also stated that 40 ng/ml was potentially dangerous, which it isn’t,” he says.
“The IOM report doesn’t actually say ‘dangerous,’” responds Ross. “It says there is no solid evidence of benefit going above 20 ng/ml, and it raises caution that new data suggest that for some people, higher levels may increase risk.”
In June 2011 the Endocrine Society, whose members are hormone specialists, weighed in with its clinical guidelines for physicians. Considered the Holy Grail of vitamin D recommendations, the Society’s guidelines generally suggested larger daily amounts of vitamin D to prevent and treat vitamin D deficiency than did the IOM: 400 to 1,000 IU for infants less than 1 year old, 600 to 1,000 IU for older children and teenagers, and 1,500 to 2,000 IU for adults. The Society also advised doctors that obese adults might need up to 10,000 IU daily for two months to correct a deficiency.
“I never see a patient whose vitamin D I don’t measure, mainly because deficiencies are so common, especially in people with serious diseases,” says Ron Hunninghake, MD, chief medical officer of the nonprofit, nutrition-oriented Riordan Clinic in Wichita, Kan. And if a patient does show up deficient in the nutrient? “I won’t let them out of the office without recommending vitamin D.”
Top 3 Benefits of Vitamin D
So, what exactly makes vitamin D so important to our health? Quite simply, it directly and indirectly influences most of what happens in our bodies every second of every day.
To understand, you have to shift your thinking a bit. Vitamin D isn’t actually a vitamin. Rather, it’s a hormone precursor that our biological ancestors made from being in the sun. When exposed to UV rays, a chemical cousin of cholesterol in the skin converts to vitamin D, which travels to the liver and is changed to the prehormone calcidiol. Calcitriol (the actual hormone) attaches to more than 2,700 sites on the human genome, and it turns on more than 1,000 genes, prompting them to do their jobs.
Creighton University’s Robert P. Heaney, MD, points out that vitamin D is a key part of the biochemical machinery that opens up our entire genome, so cells can tap into the vast information it contains. In a remarkable feat of biology, individual cells synthesize calcitriol, which then turns around to regulate those cells’ activities. It’s these fundamental roles of vitamin D that affect our risk for so many different diseases. In fact, says Heaney, “Vitamin D probably affects every disease.”
The evidence is particularly strong when it comes to vitamin D’s role in resisting infection, maintaining bone and muscle, and reducing cancer risks. (For other potential benefits, see “Vitamin D: Good for What Ails You?” sidebar.)
1. Cold and Flu Protection
Is it a coincidence that the vast majority of cold and flu outbreaks occur during the winter, when people have less sun exposure and lower levels of vitamin D? Probably not. In 2009 researchers analyzed patterns of deaths and disease complications (typically pneumonia) during the influenza pandemic that raged through the United States in 1918 and 1919, killing at least one-half million people. The researchers reported that the fewest flu deaths and complications occurred in southern cities, where the sun shone brighter throughout the year and, presumably, people had higher vitamin D levels. In contrast, the most deaths occurred in northern cities, where there was less sun exposure.
Granted, this association doesn’t prove cause and effect, but it’s certainly suggestive, and other evidence does support the protective role of vitamin D. Over the 2008–2009 winter months, doctors gave 1,200 IU of vitamin D daily to Japanese school children. Compared with children getting placebos, those taking vitamin D were 42 percent less likely to contract the flu and 83 percent less likely to suffer asthma attacks.
The underlying mechanisms are now understood. Numerous immune compounds depend on vitamin D, including PCL-gamma1, a molecule that activates immune cells so they’re capable of fighting infections. In addition, lung cells are among those that secrete 1a-hydroxylase, an enzyme that converts inactive vitamin D to its active form, helping fight respiratory infections. The vitamin D then turns on genes involved in immunity and boosts levels of cathelicidin, a powerful germ-fighting compound.
2. Stronger Bones and Muscles
Vitamin D has long been recognized as essential for normal bone formation, largely because it is essential for calcium utilization. Numerous studies have shown that the majority of seniors hospitalized for hip fractures are deficient in vitamin D.
But the problem might not be just weak bones. Heike Bischoff-Ferrari, MD, of University Hospital in Zurich, and others have made the case that weak muscles lead to falls and broken bones. The argument has its merits. Vitamin D is needed for normal muscle production and strength, and a lack of the vitamin leads to muscle weakness, a reduced range of motion, and increased physical frailty. With each passing year, seniors are more likely to be affected by sarcopenia, the age-related loss of muscle, along with osteoporosis. After analyzing 20 studies, which included more than 44,000 patients, Bischoff-Ferrari wrote in Osteoporosis International that 1,800 to 4,000 IU of vitamin D could greatly reduce the risk of falls in seniors. In contrast, the IOM recommended only 600 to 800 IU daily.
3.Lower Risk of Cancer
In 1980 epidemiologists reported that low vitamin D levels were associated with a greater risk of developing colorectal cancer.
Since then, researchers from around the world have linked low vitamin D levels to a higher risk of breast, ovarian, kidney, pancreatic and aggressive prostate cancer.
Would vitamin D supplements or greater sun exposure help protect against these cancers? The answer is yes, according to research by Cedric F. Garland, DrPH, of the University of California, San Diego.
Garland and his colleagues calculated that the incidence of colon cancer in the United States and Canada could be cut in half if people took 2,000 IU of vitamin D daily, and that women would reduce the incidence of breast cancer by half if they took 3,500 IU of vitamin D daily
How Much Should You Take?
So all this comes back to the questions: Should you take vitamin D? And if so, how much? Here’s the best advice culled from experts.
• The ideal approach is to ask your doctor for a vitamin D blood test, which will eliminate the bulk of the guesswork — but not all of it. Because of individual differences in absorption and use, people may need to take differing quantities of vitamin D to achieve a healthy blood level. Make sure your doctor orders a “25-hydroxy vitamin D” test. Other tests might result in a false normal. Although levels below 30 ng/ml indicate a deficiency, many physicians haven’t kept up with the research on vitamin D and believe that this level is just fine. The optimal level is at least 40 ng/ml and perhaps 50 ng/ml, says Heaney. But higher amounts, within reason, aren’t necessarily bad. Surfers, lifeguards and people who spend a lot of time outdoors typically have levels of 70 to 90 ng/ml.
• If you don’t currently have a significant deficiency, and if during the summer you spend a lot of time in the sun, with at least your arms and legs exposed, and you are not always slathered with sunscreen, you probably don’t need to take vitamin D supplements. Holick, who wrote The Vitamin D Solution (Hudson Street Press, 2010), suggests getting approximately 10 minutes of sun exposure (depending on time of day, season, latitudinal location and skin pigmentation) before applying sunscreen. Vitamin D made from the sun actually lasts longer in the body, compared with vitamin D from supplements or foods (also note that with the exception of wild salmon and shiitake mushrooms, most foods aren’t great sources of vitamin D).
• If it’s fall, winter or early spring, if you don’t get a lot of sun exposure, or if you know you are D-deficient, you should definitely take vitamin D supplements (most health pros recommend vitamin D3, also known as cholecalciferol). Your need will be greater if you are north of the latitude of Atlanta, since you will make little if any vitamin D from sun exposure during the months of November through March.
• If you have not taken a vitamin D blood test and you’re looking for general guidelines, Holick suggests that children take 1,000 to 2,000 IU and adults take 2,000 to 3,000 IU daily. “The bottom line for me is that there is probably no evidence that these amounts pose any risk,” he says. Cannell’s recommendation: Don’t drive yourself crazy with all the qualifications. “Just take 5,000 IU a day, unless you’re going outside to work or to the garden or beach.” The higher amount might be particularly helpful for people with a chronic illness, such as fibromyalgia, arthritis or lupus, adds Hunninghake. “These high doses of vitamin D, while generally safe, should be monitored with follow-up blood level [tests],” he says.
And what of the risks? For most people, vitamin D toxicity occurs after taking more than 40,000 IU daily for months, says Cannell. So as long as you’re being moderate in your intake, don’t sweat it.
Jack Challem is the author of more than 20 books on nutrition, including No More Fatigue: Why You’re So Tired and What You Can Do About It(Wiley, 2011), and is a member of the American Society for Nutrition.