What is the most effective dosage in vitamin D supplementation?

According to a new review from Iran significant increases in blood vitamin D concentrations are achieved with daily supplement doses of at least 800 IU for a minimum of 6 to 12 months.

The data analysis compared the increase of blood vitamin D concentrations measured in a total of 33 ran- domized controlled trials, which included adults with mean baseline vitamin D levels of 50 nmol/L who received different amounts of vitamin D3 supplements for various durations (1). The analysis showed that the increases were heterogeneous and dependent on supplementation dose, duration, baseline vitamin D level and age of the participants. With doses of at least 800 IU per day, 97.5% of participants reached levels above 50 nmol/L, with only a slight increase with higher daily doses. The increase in serum vitamin D con- centration over time reached a plateau after six months in patients with baseline levels below 50 nmol/L. In contrast, individuals with a baseline vitamin D level above 50 nmol/L required a longer duration (a mean of 12 months) to determine an accurate effect of supplementation. Higher increases of vitamin D were achieved in participants with lower baseline vitamin D concentrations. Older participants demonstrated a better res- ponse to vitamin D3 intake, independent of baseline vitamin D level.

The researchers commented that if the aim of treatment is to achieve so-called optimal levels of serum vi- tamin D (at least 75 nmol/L), individuals will need higher daily doses of vitamin D3 supplements than 800 IU. Only on the basis of bone density measurements and fall and fracture prevention in the elderly has it been suggested that the beneficial amount is likely to be 800 to 1000 IU per day (2). It has been shown that gene- tic background may play a role with regard to the response to vitamin D supplementation or diet, such as polymorphisms of the vitamin D receptor, vitamin D-binding protein, or other genetic determinates of serum vitamin D level (3, 4). While several studies have suggested that the greater effect of vitamin D supplemen- tation could be contributed to the high prevalence of vitamin D deficiency in these elderly populations, the new findings indicate that other age-related factors may also play a role.

1. Shab-Bidar S. et al. Serum 25(OH)D response to vitamin D3 supplementation: A meta-regression analysis. Nutrition. Published online June 2014.
   
2. Dawson-Hughes B. et al. Effect of calcium and vitamin D supplementation on bone density in men and women 65 years of age or older. N Engl J Med. 1997; 337:670–676.
   
3. Engelman C. D. et al. Vitamin D intake and season modify the effects of the GC and CYP2 R1 genes on 25-hydroxyvitamin D concentrations. J Nutr. 2013; 143:17–26.
   
4. Elnenaei M. O. et al. Genomic and metabolomic patterns segregate with responses to calcium and vitamin D supplementation. Br J Nutr. 2011; 105:71–79.