Vitamin D and Bones

In the last couple weeks you have seen news stories reporting a study in the New England Journal of Medicine, showing vitamin D supplements did not reduce bone fractures or osteoporosis in older adults.  This study was part of a larger trial looking at whether omega 3 fatty acids (the type found in fatty fish) and/or vitamin D could prevent cancer or heart disease in middle-aged and older adults.  So right away it’s important to note this trial was not designed to see if vitamin D can reduce the risk of fractures (or osteoporosis). The Recommended Dietary Allowance (RDA) for vitamin D in adults aged 50-70 years old is 600 IU (International Units).  For those >70 years it is 800 IU.

This study brings up an overall discussion of how we decide the amount of nutrients we should consume from food or supplements.  When the recommendations, or RDAs, were first established, the focus was on preventing nutrient deficiencies: enough vitamin A for us to see, or enough iron so we don’t become anemic.

Nutritionists now look at whether having more of these nutrients might be helpful in preventing chronic disease.  E.g. Could enough dietary fiber reduce our risk of heart disease?  Could enough vitamin D reduce the risk of osteoporosis?  Again, in general, studies looking at supplementing the diet with high levels of single nutrient – even combinations of nutrients – aren’t very effective in reducing disease risk.  However, dietary patterns containing these nutrients are associated with reduced risk of chronic diseases, so the government’s dietary guidance, the US Dietary Guidelines, continues to promote diets with a wide variety of whole, nutrient-rich foods.  It is important to note, at times we have a problem with getting enough of a nutrient (we can’t enough of a food, we can’t digest/absorb something well, we have a genetic condition or disease) and a supplement may be appropriate.  For instance, older adults may not absorb enough vitamin B-12, so are encouraged to use fortified foods or supplements with vitamin B-12.

In this study, those supplemented with vitamin D did not have a fewer fractures over the 5 years of the study than those not receiving supplements. The authors concluded: “In this randomized, controlled trial, supplemental vitamin D3 did not result in a lower risk of incident total, nonvertebral, or hip fractures than placebo among generally healthy midlife and older adults who were not selected for vitamin D deficiency, low bone mass, or osteoporosis.”  The authors are continuing work to better understand if a small proportion of people that were in the study that had low levels of vitamin D in their blood, and did not appear to benefit from the supplements, may contain people with specific genetic defects or other problems that might benefit from supplements-perhaps at a different level.

This study reinforces that healthy adults may not benefit from supplements of nutrients above those recommended.  We need to eat a healthy diet, and talk to our health care providers about whether we need any supplements.