High-dose vitamin D supplements may not increase risk of cardiovascular disease or cancer – study

Scientists have previously believed that vitamin d can increase risks of numerous illnesses if taken in large doses

Taking regular doses of vitamin D that are higher than the amount currently recommended by healthcare authorities does not increase mortality or incidence of cancer and heart disease in older people, according to a new study from the University of Eastern Finland.

Vitamin D deficiency is associated with increased risk of many diseases, including rickets. Some previous studies, however, have suggested that high doses of the vitamin may be dangerous, causing health complications.

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, the University of Eastern Finland highlighted. One of these was their own Vitamin D Trial (FIND), which took place from 2012 to 2018.

In the FIND trial, 2,495 participants (men 60 years or older and women 65 years or older) were randomised for five years to either the placebo group or the groups that received either 40 or 80 micrograms (1600 or 3200 IU) of vitamin D3 per day.

All participants were free of cardiovascular disease and cancer at the start of the trial and could use their own vitamin D supplement of up to 20 micrograms (800 IU) per day (the recommended intake for this age group when the trial began).

At the beginning and during the trial, research forms were used to collect comprehensive information from the subjects on lifestyle, nutrition, risk factors for and the incidence of diseases. They also obtained information on the incidence of diseases and on deaths from national health registers. Approximately one fifth of the randomly selected subjects underwent more detailed examinations and provided blood samples.

During the five years of the trial, 119 participants developed cardiovascular disease, 129 subjects developed cancer and 19 died. There was no statistically significant difference in the number of events between the groups. The vitamin D doses proved to be safe as no differences in side effects were observed between the groups.

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).

The findings of the FIND trial are well in line with other similar studies that have shown that taking higher doses of vitamin D than recommended for many years does not have a significant effect on the risk of developing cardiovascular disease or cancer if the body’s vitamin D status is already adequate.

In Finland, the average vitamin D intake of the population has increased since the early 2000s due to the vitamin D supplementation of vegetable oil spreads and liquid dairy products as well as the increased use of vitamin D supplements. The county also recommends a vitamin D supplementation of 10 micrograms per day (400 IU) for the adult population. The recommendation is 20 micrograms per day (800 IU) for those aged 75 and over.

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