A trial by the University of Eastern Finland found that taking a high dose of vitamin D tablets for five years did not affect total mortality or the incidence of cardiovascular disease or cancer in older men and women.
In population studies, low levels of vitamin D in the body correlated with an increased risk of many chronic diseases and premature death. However, it cannot be directly deduced from such observational studies whether the usage of vitamin D tablets can reduce the risk of chronic diseases or death.
The early 2010s saw the commencement of large-scale vitamin D trials in several countries, examining the effects of higher than recommended doses of vitamin D on the risk of developing diseases. One of the trials was the Finnish Vitamin D Trial (FIND) conducted between 2012-2018.
The FIND trial
The FIND trial was a randomised study, including 2,495 participants (men aged 60 years and older and women aged 65 years and older). The individuals were either in the placebo group or in the group receiving either 40 or 80 micrograms of Vitamin D3 per day. All participants did not have cardiovascular disease and cancer at the start of the trial and were allowed to use an additional supply of vitamin D tablets of up to 20 micrograms per day (the recommended dose for this age group at the time of the trial).
At the beginning and during the trial, research forms collected comprehensive information on lifestyle, nutrition, risk factors and the incidence of diseases of the participants. Additional information on the incidence of diseases and deaths was also obtained from national health registers. Furthermore, approximately one-fifth of the randomly selected subjects underwent more detailed examinations and provided blood samples.
High doses of vitamin D tablets have no significant effect
During the five years of the trial, 119 participants developed cardiovascular disease, 129 subjects were diagnosed with cancer, and 19 died. There was no statistically significant difference in the number of events between the groups. The vitamin D tablets dosage amount proved to be safe, as there were no differences in side effects observed between the groups.
In the sub-sample examined in more detail, the mean blood vitamin D (calcidiol) concentration was 75 nmol/L (30 ng/mL) at baseline. After one year, the mean calcidiol concentration was 100 nmol/L (40 ng/mL) in the group taking 40 micrograms of vitamin D per day and 120 nmol/L (48 ng/mL) in the group taking 80 micrograms of vitamin D per day. There was no significant change in the calcidiol concentrations in the placebo group. Only 9% of subjects had low vitamin D levels at baseline, i.e., they had a blood calcidiol concentration of less than 50 nmol/L (20 ng/mL).
Additionally, the results showed that taking high doses of vitamin D tablets for many years does not have a significant effect on developing cardiovascular disease or cancer if the vitamin D status in the body is already adequate.
In Finland, the average vitamin D intake of the population has increased since the early 2000s due to, amongst other things, the vitamin D supplementation of vegetable oil spreads and liquid dairy products as well as the increased use of vitamin D tablets.