Should you take vitamin D supplements?
My hunch is that it depends. Vitamin D is a nutrient that helps our bodies regulate the metabolism of calcium and phosphate (1). Most vitamin D comes from sunlight, while it is also found in certain foods including fatty fish, mushrooms, egg yolks, vitamin-D fortified foods. For example, milk in many countries is always fortified with vitamin D, and some brands of breakfast cereals and orange juice are fortified as well (2). Vitamin D can also be obtained through taking vitamin D supplements found at your local grocery or health food store. The classic health consequences of inadequate vitamin D are rickets in children, and low bone mineral density and osteoporosis in older adults (3). Low vitamin D has also been associated with increased risk for many other health conditions including breast, prostate, and colorectal cancer, multiple sclerosis, and cardiovascular disease (4-6). However, the quality of scientific evidence for these relationships varies because it is actually quite challenging methodologically to study the cause-effect relationship of vitamin D on health.
Because definitive high-quality evidence is lacking, the actual beneficial effect of vitamin D on health has been heavily debated in recent years. Like many other dietary or lifestyle factors that have been linked to health outcomes with scientific uncertainty (examples: coffee, alcohol, vitamin C, herbal supplements), the available information about whether to take vitamin D supplements can be very confusing. Here is where we stand right now:
In 2011, the American Institute of Medicine released an expert report on the dietary reference intakes for vitamin D (3). They stated that, for people aged 1 to 70 years old including pregnant and lactating women, the recommended dietary allowance (RDA) is 600 IU per day of vitamin D. For adults aged over 70 years the RDA is 800 IU per day. Intake should not exceed 4000 IU per day for people aged 9 years and over. The full RDA guidelines can be found here. Interestingly, their expert panel concluded that current scientific evidence is insufficient to conclude that vitamin D plays a causal role in non-bone-related health conditions (3). Now, this statement may or may not mean that vitamin D has no effect on health aside from bone conditions, simply that our current knowledge is insufficient.
