Vitamin D and Disease: A Complicated Connection
Consider the vitamin “D-tails”
Vitamin D experts reviewed 290 observational studies and 172 randomized, controlled trials to assess the effect of vitamin D blood levels and supplementation on health and disease in adults. Bone health was excluded from the review because it is well-established that adequate vitamin D is necessary for proper calcium absorption, mineral balance, and healthy bones.
The majority of observational studies linked low vitamin D levels with higher risks of a host of conditions: heart disease, elevated cholesterol, inflammation, diabetes and insulin resistance, overweight and obesity, multiple sclerosis, mood disorders, declining brain (cognitive) and physical function, infectious diseases, and death (all-cause mortality). These findings were not replicated in most of the randomized trials, in which participants supplemented with 2,000 IU or more of vitamin D per day to protect against future illness.
Further, even among people with vitamin D blood levels the National Institutes of Health defines as, “generally considered inadequate for bone and overall health in healthy individuals” (under 50 nmol/L (20 ng/mL), supplementing with 2,000 IU or more of vitamin D per day did not improve markers of health or reduce disease risk.
One group did benefit from vitamin D supplements: the elderly, particularly older women. In this group, supplementing with 800 IU or more of vitamin D daily reduced all-cause risk of death.
Don’t ditch D yet
The review suggests low vitamin D levels are a consequence of disease rather than a cause. Lead author Dr. Philippe Autier further explained that although serious diseases such as cancer may reduce vitamin D levels, that doesn’t mean raising levels with supplements would prevent disease development.
Other health experts caution that the review is not a reason to stop taking vitamin D. Dr. Nigel Belshaw of Britain's Institute of Food Research pointed out the review, “does not suggest that taking vitamin D supplements cannot be useful in some cases for some purposes. Neither does it rule out a health advantage of increasing vitamin D levels in the blood for those who are deficient.”
Keep the following in mind when fitting vitamin D into your long term health and wellness plan:
- Count age. Due to declining ability to make vitamin D in the skin and inadequate sunlight exposure, older adults are at higher risk of vitamin D deficiency. In this situation, supplements can improve health.
- Be a sleuth. If vitamin D levels are low, this may indicate underlying inflammation in the body. Work with your healthcare provider to understand why vitamin D is low, and whether other health issues need to be addressed in addition to supplementation.
- Know who’s low. Breast-fed infants, older adults, people with limited sun exposure, people with darker skin, people with inflammatory bowel disease or fat malabsorption, and those who are obese or have undergone bariatric surgery all may require vitamin D supplements to meet needs.
- Ignore the hype. Both the vitamin D “pushers” and “naysayers” promote alarmist messages, suggesting that if you don’t take vitamin D supplements you’ll risk your health, or conversely, that taking supplements will ruin your health. The truth lies somewhere in the middle: If you’re deficient, you likely can benefit from a vitamin D supplement. If you’re not, you don’t need one.
(Lancet Diabetes Endocrinol 2013, online ahead of print; available at: http://dx.doi.org/10.1016/S2213-8587(13)70165-7)