A wearable, a cold plunge and a multivitamin can all be marketed as investments in healthier years. The evidence does not give them a single verdict. Wearable activity trackers have evidence of a specific benefit: people become more active. Cold-water immersion has some specific, short-term findings, but its broader case remains preliminary or limited. For cardiovascular disease or cancer prevention, beta carotene and vitamin E fall into evidence of no benefit for a specified outcome; multivitamins fall into lack of sufficient evidence. None of those judgments is a claim that every intervention has been tested for, or disproved as a route to, longer life.
Those four distinctions matter more than a simple “works” or “doesn’t work.” They ask which outcome was measured, in whom and over what period. Here is what the research supports for three popular interventions—and where it stops.
Wearable activity trackers: an activity benefit, not a longevity result
In a 2022 umbrella review in The Lancet Digital Health, Ferguson and colleagues examined systematic reviews and meta-analyses of wearable activity trackers, including step counters and smartwatches. Across ages and clinical and nonclinical populations, trackers improved physical activity, body composition and fitness. The review translated the activity change to roughly 40 extra minutes of walking per day and reported about two pounds of weight loss. That is evidence of a specific benefit, not merely evidence that people buy devices or enjoy seeing their step counts.
The benefit has a boundary. The reviewed findings do not establish that wearing a tracker extends lifespan or healthspan; a sustained activity outcome is not a long-term survival outcome. That is lack of sufficient evidence for a longevity claim, not evidence that the observed activity gain is useless. The authors also raised concerns about measurement accuracy, obsessive behavior and inequities in who can access or benefit from the technology. A product pitch that jumps directly from a step-count change to “more healthy years” skips the outcome it needs to prove.
Cold-water immersion: timing changes the answer
Brinsley and colleagues’ January 2025 PLOS ONE systematic review and meta-analysis included 11 randomized trials with 3,177 participants. Its most specific stress finding was a significant reduction 12 hours after immersion. The review did not find a significant stress effect immediately, or at one, 24 or 48 hours. That pattern supports a time-specific short-term benefit; it does not support an undifferentiated promise that cold exposure reliably lowers stress at any moment.
Other outcomes complicate the sales pitch. Inflammation increased immediately and one hour after immersion. The health meaning of that acute response is unclear, so calling cold exposure broadly “anti-inflammatory” would misstate the measured result. The review found no significant immediate or one-hour immune-function effect. It reported improved sleep quality and quality of life, but not mood. A narrative synthesis suggested 29% less sickness absence among cold-shower participants; that finding has weaker footing than a pooled meta-analytic result and should not be treated as proof of an immune boost.
This is preliminary or limited evidence for a wider wellness claim. The authors noted few randomized trials, small samples and limited diversity. Long-term outcomes and the best immersion protocols remain unknown. A measured 12-hour stress effect can be real while a claim about extending healthy life remains unproved; likewise, a nonsignificant short-term immune result is not a definitive finding that cold water can never affect immunity.
Supplements: the purpose changes the evidence question
Supplements are often discussed as one category, but the question “Can a clinician address a documented deficiency?” is different from “Will routine supplementation prevent major disease in generally healthy adults?” The latter is what the U.S. Preventive Services Task Force assessed in its June 2022 final recommendation for community-dwelling, nonpregnant adults. Its conclusions should not be generalized to children, pregnant people, chronically ill or hospitalized people, or people with a known deficiency. The Task Force separately recommends folic acid for people planning or capable of pregnancy.
For prevention of cardiovascular disease or cancer, the Task Force recommends against beta carotene and vitamin E supplements, a Grade D judgment. This is the clearest example here of evidence of no benefit for a specified outcome; beta carotene also carried a harm signal in smokers in prior trials. It is not a verdict on correcting a deficiency, nor on every possible nutrient outcome.
For multivitamins and most other single or paired nutrient supplements, the Task Force issued a Grade I statement: evidence is insufficient to determine the balance of benefits and harms for preventing cardiovascular disease or cancer. That is lack of sufficient evidence, not a finding that benefit is impossible and not permission to advertise disease prevention as established. A supplement label can cite an ingredient’s biological role without demonstrating that taking the product prevents either disease.
Why the promise sells—and how to read it
Supplement use is common, but use is not efficacy. A CDC analysis of 2017–2018 survey data found that 57.6% of U.S. adults aged 20 and older had used any dietary supplement in the previous 30 days. A separate CDC analysis from August 2021 to August 2023 found use of two or more supplements among 23.4% of adults aged 20–39 and 56.4% of those 60 and older. The surveys measured different things and do not establish a time trend, individual motive or health payoff.
Concern about healthier years has a real population basis. In a December 2024 JAMA Network Open cross-sectional study of 183 WHO member states, Garmany and Terzic found that longer lifespans had not been matched by equivalent gains in healthy longevity. Their study describes a healthspan–lifespan gap; it cannot establish that any product closes it. Final CDC estimates put U.S. life expectancy at birth at 77.5 years in 2022, 78.4 in 2023 and 79.0 in 2024. WHO reports global life expectancy of 73.3 years in 2023 and distinguishes life expectancy from healthy life expectancy. These population measures explain the stakes, not the efficacy of a tracker, plunge or pill.
A useful reading test is to match the claim to the outcome: activity, stress after 12 hours, disease prevention or years lived in good health. Then check whether the cited study actually measured that outcome, for the relevant population and duration. A specific short-term benefit should neither be dismissed because longevity is unproved nor repackaged as proof of longevity.
