Supplements

Vitamin D

The sunlight vitamin, covered by the NIH Office of Dietary Supplements’ professional fact sheet.

Vitamin D is a fat-soluble vitamin the skin produces on exposure to sunlight and that occurs naturally in few foods. It promotes calcium absorption in the gut and is needed for normal bone mineralisation, and the National Institutes of Health Office of Dietary Supplements (ODS) fact sheet also describes roles in muscle function, nerve conduction and immune function.

What published research reports

The ODS health-professional fact sheet lists a Recommended Dietary Allowance of 600 IU (15 mcg) per day for ages 1–70 and 800 IU (20 mcg) above 70, with a tolerable upper intake level of 4,000 IU (100 mcg) per day for adults. It reports that serum 25-hydroxyvitamin D is the accepted status marker, that levels below 30 nmol/L are associated with deficiency (rickets in children, osteomalacia in adults), and that groups at risk of inadequacy include people with limited sun exposure, darker skin, older adults and people with fat-malabsorption conditions. The fact sheet states that research on outcomes beyond bone health — cardiovascular disease, diabetes, mood — has produced mixed results in large trials, and that very high intakes can cause toxicity marked by hypercalcaemia.