What supplements are really helpful?

The short version: most supplements sold for general health have thin evidence. A few help specific people in specific situations.

The evidence here is a sample of the literature, not the whole picture. But what it shows is that supplements are not general-purpose health boosters. They are targeted tools for people with a known deficiency or a clear risk.

Vitamin D is the best studied. The big trials are clear: for the general population, vitamin D alone does not prevent fractures, falls, cancer, or heart disease [1, 2]. The 2019 VITAL trial of 25,871 people found no reduction in cancer or cardiovascular events [1]. The 2018 Lancet meta-analysis of 44,790 people found no fracture reduction [1]. The only consistent benefit comes from daily vitamin D at 800-1,000 IU combined with calcium in older adults, which reduced hip fractures by about 16% [2, 3]. Even that benefit disappears with vitamin D alone, with intermittent high doses, or in people who are not deficient [3]. The 2022 meta-analysis of 32 trials found that daily 800-1,000 IU reduced fractures and falls, but only in people with baseline deficiency [3]. If your levels are normal, you are spending money for nothing.

Omega-3s are similar. Low-dose fish oil (1 gram daily) has no benefit for heart disease in any major trial [4]. The one exception is high-dose prescription EPA (icosapent ethyl, 4 grams daily) in people with high triglycerides already on a statin, which cut major cardiovascular events by 25% [4, 5]. That is a drug, not a fish oil capsule. The REDUCE-IT trial of 8,179 people showed a clear benefit, but the STRENGTH trial using a different high-dose omega-3 formulation found nothing [4]. The benefit appears specific to purified EPA at high doses, not to over-the-counter blends.

Probiotics have the best evidence for a narrow use: preventing and shortening antibiotic-associated diarrhea. The 2025 umbrella meta-analysis of 35 pediatric reviews found probiotics cut diarrhea incidence by about half [7]. A 2025 adult trial found faster resolution and fewer recurrences [6]. For H. pylori treatment, adding probiotics to antibiotics improved eradication by about 10% and reduced side effects [8]. But the effects are strain-specific, and the evidence for general gut health in healthy people is weak [9].

The pattern is consistent: supplements work best when correcting a known deficiency or addressing a specific risk. Taking them "just in case" when you are healthy and well-nourished is supported by almost no evidence from well-designed trials. The industry-funded studies that show broad benefits are contradicted by the large, independent trials.

My call: for most healthy people, no supplement is clearly helpful. The exceptions are targeted: vitamin D plus calcium for older adults at risk of deficiency, high-dose prescription EPA for high triglycerides on a statin, and probiotics during antibiotics. Everything else is marketing, not medicine. Confidence: high for the null findings in general populations, moderate for the specific benefits in targeted groups.