The VITAL study
Funded by the National Institutes of Health in the US, the randomised, placebo-controlled VITAL trial investigated whether taking daily vitamin D (colecalciferol 2000IU) and/or omega-3 (EPA/DHA 1g) reduced the risk of developing invasive cancer or major cardiovascular events (myocardial infarction, stroke, or death from cardiovascular causes) in people with no history of such diseases.
The trial recruited a total of 25,871 healthy American men and women aged ≥50 and ≥55 years, respectively, and randomly assigned them into four groups, each receiving one of the following combinations: vitamin D + omega-3, vitamin D + placebo, omega-3 + placebo, or two placebos. Participants were followed up for a median of 5.3 years.
No significant difference
Results of the primary analysis showed that neither vitamin D nor omega-3 led to a lower incidence of cancer or cardiovascular events compared with placebo.
Among the participants assigned to vitamin D (n=12,927), 793 were diagnosed with cancer compared with 824 of those assigned to placebo (n=12,944) (HR 0.96, 95% CI 0.88–1.06, p=0.47). A major cardiovascular event occurred in 396 people who took daily vitamin D, and 409 people who took the corresponding placebo (HR 0.97, 95% CI 0.85–1.12, p=0.69).
In the omega-3 group (n=12,933), 820 cancers occurred while 797 were reported in the placebo group (n=12,938) (HR 1.03, 95% CI 0.93–1.13, p=0.56). For major cardiovascular events, the corresponding numbers were 386 and 419, respectively (HR 0.92, 95% CI 0.80–1.06, p=0.24).
Strengths and limitations
The authors acknowledge the limitation of the trial duration, which may not be long enough to see the potential effects on slowly developing conditions like cancer and cardiovascular disease. However, they highlight the high rates of follow-up and adherence among other key strengths of the study.
Secondary analysis of the results suggested some potential benefits of supplementation such as fewer heart attacks in people who took omega-3 and fewer cancer deaths in people who took vitamin D; however, the authors warn that these findings should be interpreted with caution.