Vitamin D concentrations in Finnish adults have risen clearly in recent decades, according to a large-scale follow-up study conducted at the University of Oulu, Finland. This favorable development might be explained not only by the national vitamin D intake recommendations but also by the food fortification program, which has led to the addition of vitamin D to liquid dairy products and fat spreads. This finding reinforces the perception of the benefits of the use of vitamin D supplements and the food fortification program.
The storage form of vitamin D is calcidiol. Calcidiol concentrations are widely used to assess the vitamin D status of the body. The study showed that, between the 1990s and the 2010s, adult serum calcidiol concentrations increased on average by 10.6 nanomoles per liter. The seasonal variation in vitamin D concentrations also stabilized during the monitoring period.
The study also unexpectedly found that vitamin D fortification of fat spreads did not have the same effect on vitamin D concentrations in the blood as the addition of vitamin D to milk. According to the researchers, the vitamin D fortification of fat spreads might need to therefore be reassessed in the future.
The topic was studied in Northern Finland among the birth cohort born in 1966 when the subjects were 31 and 46 years of age. The study involved a total of 3,650 subjects.
The subjects with the lowest vitamin D concentrations at the start of the monitoring experienced the most marked increases in vitamin D concentrations. The result indicates that vitamin D supplements might be particularly important in preventing very low vitamin D concentrations.
"The use of vitamin D supplements and the addition of vitamin D to dairy products are useful measures at the population level and especially beneficial for people with very low vitamin D concentrations. On the basis of our research, these measures should be continued in the future," state researchers Helmi Ikonen and Johanna Lumme.
Evidence was also found of the benefits of eating fish.
Eating fish according to the guidelines, i.e. at least twice a week, had a positive effect on vitamin D concentrations in the body."
Helmi Ikonen, Researcher, University of Oulu
Vitamin D is known as an important vitamin for bones, and its deficiency has been linked in previous studies to several diseases, such as infections, diabetes, cancer, circulatory diseases, and neurodegenerative diseases.
Many Finns still get too little vitamin D, especially during the dark winter season, when vitamin D is not formed naturally on the skin as it is in summer due to lack of sunlight. Vitamin D intake is sufficient if the concentration of vitamin D in the blood is between 75 and 120 nanomoles per liter.
In addition, the study showed that not only vitamin D intake but also genetics, behavioral and socioeconomic factors may influence individual vitamin D concentrations.
The study is one of the largest follow-up studies of vitamin D concentrations, and it shows the effects of national food policy and the vitamin D intake recommendations in the adult population.
The study was recently published in the European Journal of Nutrition.
Ikonen, H., et al. (2021) The determinants and longitudinal changes in vitamin D status in middle-age: a Northern Finland Birth Cohort 1966 study. European Journal of Nutrition. doi.org/10.1007/s00394-021-02606-z.