We came across this tweet posted on 6 October that has received over 1600 likes and more than 450 retweets at the time of writing:
According to the tweet, provided with no evidence whatsoever, Vitamin D is the single most effective medicine against cancer, being far more beneficial than any cancer drug known to modern science. Vitamin D, also known as calciferol is most commonly produced when ultraviolet (UV) rays from sunlight strike the skin and trigger Vitamin D synthesis but can also be found in food like fish liver oil and the flesh of fatty fish (such as trout, mackerel and salmon).
A check on the claim unsurprisingly found no sources that point to Vitamin D being an effective medicine against cancer, let alone the single most effective treatment against cancer. Instead, we found an evidence based review published in 2022 by the US Preventive Services Task Force, an independent, volunteer panel of national experts in prevention and evidence-based medicine.
The report, which tested the efficacy of supplementation with single nutrients or multivitamin supplementation found that Vitamin D was not associated with any changes in cancer mortality or incidence. It concluded that more studies were needed to be conclusive however, with the available studies on Vitamin D and its effect on cancer mortality not having been conducted with sufficient duration.
Based on currently available evidence then, the claim that Vitamin D is the single most effective medicine against cancer is false.