By late winter 2023, 7 to 26 per cent of the Dutch population had vitamin D deficiency. This is the outcome of a study conducted by RIVM. Because the Netherlands has so little sunlight in winter, this is when the so-called vitamin D status (amount of vitamin D in the body) is at its lowest. For this study, blood from participants of the Lifelines cohort, a large population-based cohort study in the northern Netherlands, was examined. According to the study, men were more likely to have a deficiency than women, and blood levels of vitamin D increased with age.
The study was recently published in the scientific journal European Journal of Clinical Nutrition. The study also shows that the Dutch population had a higher vitamin D status in March 2023 than in March 2011. Data on the vitamin D status from 2011 shows that vitamin D deficiency goes down to 0–5 per cent in the summer months because there is more sunlight. This is therefore expected to be the same in 2023. The health effects of (annual) short-term vitamin D deficiency in winter are still unclear. Furthermore, no data on factors that may have influenced the increased vitamin D status compared to 2011 was available within the Lifelines cohort. Such factors include supplement use or exposure to sunlight These possible explanations, therefore, cannot be substantiated based on this study. In a follow-up study, it would be important to look at the influence of such factors.
Advice on supplement use
To ensure a sufficient vitamin D intake for everyone, the Health Council of the Netherlands has advised some groups to take vitamin D supplements. This advice is aimed at, among others, women over 50 and men over 70. This RIVM study shows that these groups had the most vitamin D in their blood. One of the explanations for the higher vitamin D status in 2023 compared to 2011 might be the Health Council's most recent adjustment of its advice on supplements in 2012. Whether this actually means that people followed the advice on supplements cannot be concluded based on the data in this study. The latest Food Consumption Survey (VCP) shows that women use supplements more often than men. This could partly explain the higher vitamin D status in women.
Population-based cohort study in the northern Netherlands
The Lifelines cohort is a large population-based cohort study in Groningen, Friesland and Drenthe. This cohort study follows participants of different ages and backgrounds for an extended period of time. For this study, RIVM looked at a group of adult participants whose blood was drawn in March 2023. Within the Lifelines cohort, blood levels of vitamin D had been measured once before, in 2011. It was possible to compare this data with the 2023 results.
Recommendations for further studies
In addition to studies on the health effects of short-term vitamin D deficiency and factors contributing to vitamin D status, studies on the vitamin D status of other groups for which an advice on supplements has been issued would also be desirable. Examples are pregnant women and adults with dark skin tones. RIVM is currently preparing a study on the vitamin D status of these groups, commissioned by the Dutch Ministry of Health, Welfare and Sport. In addition, RIVM is also conducting a study into the extent to which people have complied with the advice on supplements. The results of this study, combined with the results of this vitamin D status study, may give rise to a recommendation on adjustments in policy or the way information is provided.