As the days get shorter and we head into winter, your chances of being deficient in this crucial vitamin skyrocket.
Known as "the sunshine vitamin," vitamin D is produced in our skin when exposed to ultraviolet rays from the sun. But this source is in short supply throughout late fall and winter. During this time, the sun is so weak in most of the country that our bodies make no vitamin D at all.
Even during summer months, with the increased use of sunscreen to protect our skin, research shows that many of us don't get the vitamin D we need. In fact, a recent Harvard Study found that 60% of Americans may be vitamin D deficient. Another study found that 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.
Numerous studies in the news recently have linked vitamin D deficiencies to everything from cancer, cardiovascular disease and diabetes to dementia, obesity, and even death. Here are just a few:
• The most well-known role of Vitamin D is in bone health. 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 cancer, and numerous studies in the past few years have supported that relationship. In fact, the Canadian Cancer Society has made a first ever supplement recommendation for vitamin D, based on the increasing evidence about the link between vitamin D and reducing risk for colorectal, breast and prostate 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 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.
• 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.
How do you know if you are deficient? A simple blood test – the 25(OH)D or calcidiol test – can tell your doctor whether your vitamin D level is low. The U.S. National Institutes of Health notes that 25(OH)D levels over 30 ng/mL are optimal, while the Vitamin D Council recommends that 25(OH)D levels be between 40 and 65 ng/mL
The current recommended daily dose of vitamin D is 200 IU for people up to age 50, 400 IU for people aged 51 to 70, and 600 IU for people over age 70. But those numbers are due to change; US and Canadian governments are sponsoring a US Institute of Medicine review of the issue, to be completed the summer of 2010.
Most experts (including the Canadian Cancer Association) agree adults should take in 1,000 to 1,400 IU a day, and the Vitamin D Council recommends that healthy adults take 2,000 IU of vitamin D daily. The American Academy of Pediatrics recently doubled the amount of vitamin D all children should get, to 400 IU every day.
Vitamin D is naturally present in very few foods (such as oily fish, liver and egg yolks), although milk and some foods and juices are fortified with Vitamin D. Many health experts, including Harvard Medical School, now agree that dietary supplements are the key way to meet daily vitamin D requirements.
Basic Nutrient Support contains 400 IU of vitamin D in each daily serving, and Bone Support supplies an additional 800 IU.