How does light-intensity physical activity associate with adult cardiometabolic health and mortality? Systematic review with meta-analysis of experimental and observational studies

Aim To assess the relationship between time spent in light physical activity and cardiometabolic health and mortality in adults. Design Systematic review and meta-analysis. Data sources Searches in Medline, Embase, PsycInfo, CINAHL and three rounds of hand searches. Eligibility criteria for selecting studies Experimental (including acute mechanistic studies and physical activity intervention programme) and observational studies (excluding case and case-control studies) conducted in adults (aged >= 18 years) published in English before February 2018 and reporting on the relationship between light physical activity (<3 metabolic equivalents) and cardiometabolic health outcomes or all-cause mortality. Study appraisal and synthesis Study quality appraisal with QUALSYST tool and random effects inverse variance meta-analysis. Results Seventy-two studies were eligible including 27 experimental studies (and 45 observational studies). Mechanistic experimental studies showed that short but frequent bouts of light-intensity activity throughout the day reduced postprandial glucose (-17.5%; 95% CI -26.2 to -8.7) and insulin (-25.1%; 95% CI -31.8 to -18.3) levels compared with continuous sitting, but there was very limited evidence for it affecting other cardiometabolic markers. Three light physical activity programme intervention studies (n ranging from 12 to 58) reduced adiposity, improved blood pressure and lipidaemia; the programmes consisted of activity of > 150 min/week for at least 12 weeks. Six out of eight prospective observational studies that were entered in the meta-analysis reported that more time spent in daily light activity reduced risk of all-cause mortality (pooled HR 0.71; 95% CI 0.62 to 0.83). Conclusions Light-intensity physical activity could play a role in improving adult cardiometabolic health and reducing mortality risk. Frequent short bouts of light activity improve glycaemic control. Nevertheless, the modest volume of the prospective epidemiological evidence base and the moderate consistency between observational and laboratory evidence inhibits definitive conclusions.