An article in the American Journal of Clinical Nutrition has looked at how much dietary vitamin D is necessary to ensure adequate serum concentrations over the winter months. The target vitamin D level was taken to be 25 nmol/L, and the daily doses required to maintain this ranged from 7.2 mcg/day to 41.1 mcg/day, depending on the subject in question’s taste for sunshine.

This correlates to a range between 288 IU and 1,644 IU, where 1 IU = 25 ng.

Personally, I supplement with 4,000 IU/day cholecalciferol, so I assume I am in the ’safe’ zone.

Here is the abstract for your perusal:

Estimation of the dietary requirement for vitamin D in healthy adults.

Am J Clin Nutr. 2008 Dec;88(6):1535-1542. PMID: 19064513

Cashman KD, Hill TR, Lucey AJ, Taylor N, Seamans KM, Muldowney S, Fitzgerald AP, Flynn A, Barnes MS, Horigan G, Bonham MP, Duffy EM, Strain J, Wallace JM, Kiely M.

Departments of Food and Nutritional Sciences, University College, Cork, Ireland, and the Northern Ireland Centre for Food and Health, University of Ulster, Coleraine, United Kingdom.

BACKGROUND: Knowledge gaps have contributed to considerable variation among international dietary recommendations for vitamin D. OBJECTIVE: We aimed to establish the distribution of dietary vitamin D required to maintain serum 25-hydroxyvitamin D [25(OH)D] concentrations above several proposed cutoffs (ie, 25, 37.5, 50, and 80 nmol/L) during wintertime after adjustment for the effect of summer sunshine exposure and diet. DESIGN: A randomized, placebo-controlled, double-blind 22-wk intervention study was conducted in men and women aged 20-40 y (n = 238) by using different supplemental doses (0, 5, 10, and 15 mug/d) of vitamin D(3) throughout the winter. Serum 25(OH)D concentrations were measured by using enzyme-linked immunoassay at baseline (October 2006) and endpoint (March 2007). RESULTS: There were clear dose-related increments (P < 0.0001) in serum 25(OH)D with increasing supplemental vitamin D(3). The slope of the relation between vitamin D intake and serum 25(OH)D was 1.96 nmol.L(-1).mug(-1) intake. The vitamin D intake that maintained serum 25(OH)D concentrations of >25 nmol/L in 97.5% of the sample was 8.7 mug/d. This intake ranged from 7.2 mug/d in those who enjoyed sunshine exposure, 8.8 mug/d in those who sometimes had sun exposure, and 12.3 mug/d in those who avoided sunshine. Vitamin D intakes required to maintain serum 25(OH)D concentrations of >37.5, >50, and >80 nmol/L in 97.5% of the sample were 19.9, 28.0, and 41.1 mug/d, respectively. CONCLUSION: The range of vitamin D intakes required to ensure maintenance of wintertime vitamin D status [as defined by incremental cutoffs of serum 25(OH)D] in the vast majority (>97.5%) of 20-40-y-old adults, considering a variety of sun exposure preferences, is between 7.2 and 41.1 mug/d.