Don't take a multivitamin to live longer or prevent heart and blood vessel disease

High value
Evidence A
Saves money
Disputed
Free
Takes minutes
No willpower

In plain words

14,000 (1.4万) male doctors took a multivitamin for eleven years. As many of them had a major heart or blood vessel event or died as among those who did not take it. When 9 trials with more than 50,000 (5万) people are looked at together, there is also no visible effect on death. Skipping it saves 200 to 700 CNY a year. People who have been found to be truly deficient in a nutrient, and pregnant women taking folic acid, are not covered by this item.

Cost: About 0.5 to 2 CNY a day, 200 to 700 CNY a year. It takes no time, just one pill. After a while it is easy to feel dependent on it, as if skipping a day means you left something undone.
What you get: The PHS II trial enrolled 14,641 male doctors and followed them for 11.2 years (a median: half were followed longer, half shorter). The share who had a major heart or blood vessel event was the same among those who took it and those who did not. Major cardiovascular events HR 1.01 (HR is the hazard ratio; 1 means the two sides are the same). 95% CI 0.91–1.10 is the plausible range for that number. Death was the same too: all-cause death HR 0.94 (0.88–1.02). The U.S. Preventive Services Task Force (USPSTF), which grades preventive measures, in 2022 pooled 9 randomized controlled trials with 51,550 people and found no link between multivitamins and total deaths. Its grade was I, meaning the evidence is insufficient to say. It looks like a good deal because “one pill fills in every nutrient” sounds smooth, and it costs only a few tenths of a CNY a day
Notes: Dispute: cancer was also examined in the same group of male doctors. The share who developed cancer was about 8% lower among those who took it (0.86–0.998, P=0.04, barely over the line for “unlikely to be chance”). The share who died of cancer was about 12% lower (0.77–1.01). That range crosses 1, so it may be just chance. The benefit is small, and has only been seen in male doctors. People found to be truly deficient in a nutrient, pregnant women (folic acid), and people whose diet is very narrow are not covered; follow your doctor for them
Evidence grade: A : Specific numbers from meta-analyses, large cohorts or randomized trials; for law and policy, the statute or official text.
Sources: Sesso HD et al. (2012). Multivitamins in the prevention of cardiovascular disease in men: the Physicians' Health Study II randomized controlled trial. JAMA. https://doi.org/10.1001/jama.2012.14805
US Preventive Services Task Force (2022). Vitamin, Mineral, and Multivitamin Supplementation to Prevent Cardiovascular Disease and Cancer. JAMA. https://doi.org/10.1001/jama.2022.8970
Gaziano JM 等 (2012). Multivitamins in the Prevention of Cancer in Men. JAMA. https://doi.org/10.1001/jama.2012.14641（备注里那项癌症结果）

Translated from the Chinese original. Original book, section 6, tip 1. Content may be out of date and rules differ by place. When you actually deal with an agency, a doctor or a court, follow what local officials, doctors and lawyers tell you. Disclaimer