Research says you need more vitamin D than what you get from being outdoors. Read on to soak up why you should be diligent about ingesting this nutrient
Elizabeth M. Ward, M.S., R.D.
We always seem to be hearing about a vitamin or a mineral having its 15 minutes of media fame, and vitamin D is the latest to hit the spotlight. In fact, recent research transforms what was once a sunshine-driven vitamin into one that should be supplemented into your diet. Here are six roles this important vitamin plays in your quest for an active and healthy life.
As nutrients go, vitamin D is a rarity: It’s one of only two vitamins your body makes on its own. The liver, kidneys and cells in several other parts of the body convert two forms of vitamin D to its active form, the steroid hormone 1,25-dihydroxyvitamin D, and any extra is stored in fat tissue for future use. Vitamin D2 (ergocalciferol) is found in plant sources and can enter the body only through what you eat. The more potent vitamin D3 (cholecalciferol), which can be produced through sun exposure, from animal products or supplementation, tends to be more readily converted to the active form in the body.
In theory, we can make all the vitamin D we need; in reality, we don’t. “About half of all Americans are chronically deprived of vitamin D,” says Michael F. Holick, PhD, MD, director of the Vitamin D, Skin and Bone Research Laboratory at Boston University. Living in northern climates is a problem because sunshine is weak for about half the year, but that doesn’t mean sunnier locales fare better. Slathering on sunscreen with an SPF of 8 or higher blocks the ultraviolet B rays that generate vitamin D production. In addition, relatively few foods provide vitamin D.
D IS A GERM BUSTER
Colds, flu and other respiratory problems are more common during the winter months, coinciding with the time of year when people are most deficient in vitamin D. Holick says D plays a role in revving up the immune system by boosting the activity of cells that battle bacteria and viruses all year long.
In related research, a study in the the Journal of Clinical Investigation found that fluctuations in vitamin D3 levels can affect a skin wound’s ability to heal. “Our study shows that skin wounds need vitamin D3 to protect against infection and begin the normal repair process,” says Richard L. Gallo, MD, PhD, professor of medicine and chief of University of California, San Diego’s Division of Dermatology. “A deficiency in active vitamin D3 may compromise the body’s innate immune system that works to resist infection, making a patient more vulnerable to [bacteria].”
D IS A BONE BUILDER
There’s a reason why milk has added vitamin D: Calcium needs it to build strong bones and help you escape osteoporosis down the road. Without vitamin D, calcium would be nearly useless since it regulates calcium’s absorption from food and supplements and directs its movement in and out of bones. “In the absence of adequate vitamin D, only 10–15 percent of dietary calcium is absorbed by the body,” Holick says — much less than the typical 30 percent when enough vitamin D is present.
Inadequate levels of vitamin D also play a role in osteomalacia, the adult version of rickets, a condition characterized by unrelenting bone pain, muscle aches and muscle weakness. Osteomalacia makes it difficult to work out and, as a result, may lead to weight gain and loss of muscle tissue. Overweight people are particularly prone to the condition because excess fat absorbs vitamin D and makes it unavailable to nurture bones and muscle.
D IS A DISEASE FIGHTER
A study from the Harvard School of Public Health (Boston) found that people with the highest blood levels of vitamin D had a 62 percent lower risk of developing multiple sclerosis (MS), an autoimmune disorder that often strikes women and occurs when the body attacks the nervous system. It also found that vitamin D offered the strongest protection in people younger than 20. This study adds to evidence from an earlier Harvard investigation in which women who took at least 400 IU of vitamin D were 40 percent less likely to develop MS compared to those taking no supplements.
Despite the positive results, researchers are cautiously optimistic about D’s ability to ward off MS. “It’s too early to recommend vitamin D as a way to prevent MS in the general public,” says Kassandra Munger, MS, a doctoral candidate at Harvard and a study author. “Vitamin D is good for overall health, but it’s no magic bullet.”
D MAY BE A CANCER PREVENTATIVE
Ironically enough, sunshine keeps cancer in check. In fact, some sunshine may actually do more good than harm. A study in the American Journal of Preventive Medicine found that women living in sunnier regions of the world had a significantly lower risk of contracting ovarian cancer than those living in colder climates. Researchers concluded that the difference in sun exposure — which accounts for discrepancies in blood vitamin D levels — may be why living in southern regions offers protection.
Other research links a reduced risk of colon cancer to greater sunshine exposure. The results are encouraging, but they still don’t confirm that vitamin D prevents the cancers studied.
D IS A MUSCLE BUILDER
Considering that vitamin D actually gets converted in the body to a steroid hormone, it makes sense that it would affect muscle tissue. The active form of vitamin D binds to specific receptors found on muscle cell membranes and in muscle cell nuclei. When it binds to these receptors, it enhances muscle contraction and protein synthesis — the buildup of muscle protein. Research shows that certain types of these receptors may be responsible for greater muscle size and strength. Although you can’t alter the type of vitamin D receptors you have in your muscles, making sure you have adequate levels of vitamin D in your body can help ensure that your muscle vitamin D receptors are activated for optimal muscle function, strength and growth.
D IS A BRAIN BOOSTER
You may be sharp, witty and intelligent now, but if you’re deficient in vitamin D, you may not be so in old age. Psychiatric and neurologic disorders have been traced to low levels of vitamin D.
A study from the Washington University School of Medicine (St. Louis) and published in the American Journal of Geriatric Psychiatry examined the relationship of vitamin D levels, cognitive performance and mood in older adults. Researchers found that vitamin D deficiency was associated with depression and diminishing cognitive performance.
HOW MUCH IS ENOUGH?
While some experts are tentative, it’s difficult to deny the potential power of vitamin D. Taking in more than the recommended daily allowance — 200 IU per day — is attractive considering that supplementation involves very little risk. Holick recommends consuming 1,000 IU daily as cholecalciferol (vitamin D3), the most beneficial form. Dark-skinned people in particular should consider taking vitamin D supplements because melanin acts as a natural sunscreen, limiting their bodies’ ability to produce it. As with most supplements, you can get too much of a good thing, so limit your intake to 2,000 IU per day. And while research points to supplementation as one of the best ways to get enough D, don’t use that as an excuse not to eat a balanced diet.