Avoiding winter vitamin D deficiency takes 12 µg a day, higher targets take far more

How much vitamin D people need each day is one of the most argued-over numbers in nutrition, and the answer hinges on winter, when sunlight cannot top up the body's stores and intake has to do the work alone. Official reference values have mostly been derived by pooling the average results of trials, but averages hide how differently individuals respond to the same intake. The researchers argue that analysing the raw data from every participant is a better way to capture that between-person variability, and set out to re-derive dietary reference values for vitamin D on that basis, using trials of fortified foods rather than supplements.

The team identified 11 randomised controlled trials of foods fortified with vitamin D3 through a systematic search with predefined eligibility criteria. They then obtained the individual data for all 1429 participants, whose ages ranged from 2 to 89 years. Using these records they modelled how winter blood levels of 25-hydroxyvitamin D, the standard marker of vitamin D status, respond to total vitamin D intake. From those models they estimated the daily intakes needed to keep given proportions of the population above blood-level thresholds of 25, 30 and 50 nmol/L, running the sums both unadjusted and adjusted for baseline levels, age and body mass.

Keeping 97.5% of people above the 25 and 30 nmol/L thresholds in winter required intakes of just 6 and 12 µg a day respectively. The 50 nmol/L threshold was far more demanding: holding 90%, 95% and 97.5% of people at or above it required 33.4, 57.5 and 92.3 µg a day in the unadjusted model, falling to 17.0, 28.1 and 43.6 µg a day once baseline levels, age and body mass were accounted for. Crucially, these individual-level estimates for the 50 nmol/L target came out much higher than those produced by the standard approach of pooling trial averages, which cannot capture how much people differ from one another.

This analysis strengthens the case that an intake of 12 µg a day, achievable through food-based approaches such as fortification, could prevent vitamin D deficiency, defined here as blood levels below 30 nmol/L, across the general population. It also complicates the picture for the more ambitious 50 nmol/L target, because the intakes needed to get nearly everyone there are substantially higher than aggregate methods had suggested. That gap matters for how reference values are set, since the method itself changes the answer. The open question it leaves is a scientific and policy one: which blood threshold should populations actually be aiming for, since the cost of the higher target is steep.

If you have ever wondered why vitamin D advice varies so widely, this analysis shows the honest reason: the required intake depends on which blood level you treat as the goal, and the numbers diverge sharply. Avoiding outright winter deficiency looks achievable for nearly everyone at a modest 12 µg a day, the kind of amount fortified foods can supply. Reliably reaching the higher 50 nmol/L level across a whole population would take several times more, and individual responses vary enough that averages mislead. This is information for understanding the debate, not a prescription; intake decisions sit with you and, where relevant, your doctor.