Re: Vitamin D does not reduce cancer or cardiovascular events in healthy adults, trial finds
But vitamin D reduces cancer and cancer mortality in deficient adults
The crucial point of the vitamin D discussion is: What level of serum 25(OH)D do we call sufficient or healthy? Is it 25, 50 or 75 nmol/l? If we want to evaluate whether taking vitamin D and repleting serum levels to normal is beneficial, then we must first define "deficiency", then take deficient individuals and conduct a trial giving a sufficient amount of supplement to one group or placebo to the other group. Most vitamin D researchers define the cut off for sufficiency as 50 to 75 nmol/l, not any longer 25 nmol/l (as SACN still does (1)).
In VITAL (2) most participant of both groups were not vitamin D deficient (assuming 50 nmol/l as sufficiency), because all participants lived in the US, where the average 25(OH)D level is around 50 nmol/l and most participants were therefore replete (US has widespread fortification). It meant results are not as clear cut as they could have been, they were "noisy results”.
In contrast, in the UK average serum 25(OH)D levels are lower than in the US (1) and a similar trial conducted in the UK might have produced more positive headlines.
But despite the negative headlines, in VITAL slim people, BMI < 25, did have less invasive cancers, hazard ratio 0.76 (0.63–0.90), with vitamin D supplements. More obese people might have needed a higher dose of vitamin D, as the authors also discussed.
In addition, death from all cancers was significantly lower with vitamin D than with placebo , in a secondary analysis, hazard ratio, 0.75 [95% CI, 0.59 to 0.96].
As GP I observed in the last 10 years that vitamin D supplementation for our cancer patients had clearly beneficial effects including surprisingly long survival in individual cases.
I feel it cannot be concluded from VITAL that vitamin D does not play a role in reducing cancer incidence or cancer mortality in vitamin D deficient individuals. This could particularly be important in the UK with her lower serum 25(OH)D levels.
(1) SACN 2016 Vitamin D and health. https://www.gov.uk/government/groups/scientific-advisory-committee-on-nu...
(2) Manson JE, Cook NR, Lee IM, et al. VITAL Research group. Vitamin D Supplements and Prevention of Cancer and Cardiovascular Disease. November 10, 2018, at NEJM.org.
Competing interests: No competing interests