Vitamin D has long been associated with bone health, but numerous recent studies have linked vitamin D deficiencies to everything from cancer, cardiovascular disease and diabetes to dementia, obesity, and even death.
Known as "the sunshine vitamin," vitamin D is produced in our skin when exposed to ultraviolet rays from the sun. But with less time spent outdoors and increased use of sunscreen, most people do not receive enough exposure to produce adequate amounts of vitamin D. Dark skin and obesity can further block the production of vitamin D, and people living in northern latitudes get even less UV exposure than others.
Because of these factors, it is estimated that 77% of the adult population has insufficient vitamin D levels, and it is often hard to tell when you are deficient (ask your doctor to get tested; your blood levels should be 30 ng/mL or higher). In addition, 7 out of 10 kids are not getting enough vitamin D, putting them at risk as they develop.
And with vitamin D playing a role in bone, heart, mental, immune, and overall health, deficiency in this "wonder" vitamin can have devastating effects.
• The most well-known role of Vitamin D is in bone health. A fat-soluble vitamin, it enhances the absorption of dietary calcium and phosphorous, and stimulates the synthesis of bone tissue. Low levels of Vitamin D can lead to or worsen osteoporosis, osteopenia and rickets, and increase the risk of bone fractures.
• It has long been believed that vitamin D was associated with a reduced risk of certain cancer – including prostate, breast and pancreatic – and numerous studies in the past few years have supported that relationship. Low vitamin D also seems to increase risk for colon and GI cancers.
• A growing body of evidence suggests that vitamin D deficiency may negatively affect the cardiovascular system, above and beyond established cardiovascular risk factors. Harvard researchers found that men with vitamin D deficiency were 142% more likely to suffer from a heart attack than men with sufficient levels of the vitamin.
• Vitamin D reduces inflammation, which could explain its heart-protective role, and also helps with joint and muscle pain.
• Vitamin D plays an important role in immune function, protecting against flu, colds and respiratory infections (see Dr. Cherry's Protecting Yourself Against H1N1 Flu video). Deficiencies are also linked to an increased risk of developing autoimmune and infectious diseases, indicating that vitamin D may play an important role as an immune balancer.
• Vitamin D may improve insulin resistance and sensitivity, both of which are risk factors for diabetes. Studies have shown a relatively consistent association between low intakes of calcium, vitamin D, or dairy intake and type-2 diabetes.
• Vitamin D may affect mood and mental function. Increased intakes may slow age-related losses in mental function and may lead to mood improvements and protect against depression.
• Two recent studies have shown that that low blood levels of the sunshine vitamin are associated with increased risk of mortality from all causes, and mortality from heart disease.
Vitamin D is naturally present in very few foods (such as oily fish, liver and egg yolks), and even fortified foods don't supply adequate amounts (fortified milk is most common source, and it provides only 100 IU per cup).
Many health experts, including Harvard Medical School, now agree that dietary supplements are the key way to meet daily vitamin D requirements. Recommended daily intakes had been 200-600 IU daily, depending on age, but that is set to be increased. The American Academy of Pediatrics recently doubled the amount of vitamin D all children should get, to 400 IU every day, and a government-sponsored US Institute of Medicine review of recommended vitamin D supplementation is scheduled to be completed this summer.
Most experts, including Dr. Cherry, recommend 1,000-2,000 IU daily, for optimal benefits. The most effective form for supplementation is vitamin D3, or cholecalciferol, rather than the less potent D2 form.