With the use of vitamin D supplements growing more widespread, researchers have investigated the effect of long-term supplementation.
According to researchers writing in the journal, Clinical Nutrition, the use of high-dose vitamin D supplementation has increased in recent years. However, relatively little is known about the safety of long-term high doses.
And so, they set out to investigate the safety of a monthly high-dose of vitamin D3 supplementation taken for up to four years. Data were collected in a randomised, double blind, placebo-controlled trial of 5,108 adults aged 50-84 from Auckland, New Zealand. Participants were given monthly doses of 100,000 IU vitamin D3 or placebo, for a median of 3.3 years. They answered an open-ended question in a monthly questionnaire about any adverse events they attributed to the study capsules, which were coded blindly. Incidence rates per person months were calculated for categories of adverse events. Cox regression model used to calculate hazard ratio of time to first adverse-event.
The results revealed that 419 (16.5 per cent) of participants taking vitamin D and 399 (15.8 per cent) taking placebo reported one or more adverse event. Compared to placebo, the hazard ratio (HR) of reporting first adverse event in the vitamin D group was 1.03. And despite a slightly higher incidence of recurrent adverse events in the vitamin D arm, the incidence rate ratio (1.17) was not significantly higher in vitamin D.
In conclusion, the researchers said: “Monthly supplementation of 100,000 IU vitamin D3 for a median of 3.3 years did not affect participant-reported adverse events.”