150 minutes a week buys less heart protection than you think

The familiar advice to get 150 minutes of moderate-to-vigorous activity each week sits at the heart of nearly every public health guideline, yet how much protection that dose actually delivers has been surprisingly unclear. It is also uncertain how activity interacts with cardiorespiratory fitness, since two people doing the same weekly minutes can have very different fitness levels. This study set out to map the joint dose-response of tracker-measured activity and fitness against heart disease, and to test with genetic methods whether the relationships look causal rather than merely correlational.

Researchers followed 17,088 UK Biobank participants whose moderate-to-vigorous activity was measured with wrist accelerometers and whose cardiorespiratory fitness was estimated as VO2max. Activity data were linked to hospital and death registries to capture new cases of cardiovascular disease, including atrial fibrillation, heart attack, heart failure and stroke. A statistical model traced the joint, non-linear relationship between activity, fitness and disease risk while adjusting for confounders. Alongside the cohort work, the team ran two-sample Mendelian randomisation analyses using genetic summary data for activity traits and fitness to probe potential causal effects.

Over a median follow-up of 7.85 years, 1233 cardiovascular events occurred, and activity and fitness interacted non-linearly. Meeting the 150 minutes a week guideline was associated with a modest 8%-9% lower risk across fitness levels, whereas achieving a risk reduction beyond 30% required threefold to fourfold higher volumes, roughly 560-610 minutes a week. Fitness beyond what activity and other factors predicted kept a small protective association, a hazard ratio of 0.98 per 1 mL/kg/min. In the genetic analyses, higher fitness was linked to lower heart failure risk with an odds ratio of 0.79, while genetic evidence for activity traits was weaker and less consistent.

This work complicates the comfortable reading of activity guidelines as a finish line. It agrees with earlier evidence that any activity helps, but it sizes the guideline dose honestly as a modest safety margin rather than optimal protection, and it adds a fitness-stratified matrix of weekly targets. The genetic findings strengthen the case that cardiorespiratory fitness matters in its own right, echoing prior cohort work. Open questions remain: activity was measured at a single point, the cohort skews healthy and European, and observational and genetic methods each carry their own assumptions about causality.

This is a reason to see 150 minutes a week as a floor rather than a ceiling: the association at that dose was real but modest, and larger risk reductions tracked with substantially higher volumes. It is also a reason to think fitness itself, not just minutes logged, carries independent weight for heart health, since the genetic evidence was strongest for cardiorespiratory fitness. None of this shows that the guideline is wrong, only that the protection it buys appears smaller than many assume and that the dose-response curve keeps climbing well beyond it.