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 isnít actually a vitamin. Rather, itís 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 Universityís 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 cellsí activities. Itís 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 Dís role in resisting infection, maintaining bone and muscle, and reducing cancer risks.
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 itís certainly suggestive, and other evidence does support the protective role of vitamin D. Over the 2008Ė2009 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 theyíre 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? Hereís the best advice culled from experts.
ē The ideal approach is to ask your doctor for a vitamin D blood test, which will eliminate the bulk of the guesswork ó 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 ď25-hydroxy vitamin DĒ test. Other tests might result in a false normal. Although levels below 30 ng/ml indicate a deficiency, many physicians havenít 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, arenít necessarily bad. Surfers, lifeguards and people who spend a lot of time outdoors typically have levels of 70 to 90 ng/ml.
ē If you donít 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 donít 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 arenít great sources of vitamin D).
ē If itís fall, winter or early spring, if you donít 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.
ē If you have not taken a vitamin D blood test and youíre 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. Cannellís recommendation: Don’t drive yourself crazy with all the qualifications. “Just take 5,000 IU a day, unless youíre 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.