Commentary on: Associations of accelerometer-measured light-intensity physical activity with mortality and incidence of cardiovascular disease and cancers: A prospective UK Biobank cohort analysis

Light-intensity physical activity (LPA, 1.6‒2.9 metabolic equivalents (METs)) has been shown to reduce the risk of premature mortality;^1,2 however, little is known about the minimum and optimal weekly volume of LPA associated with this benefit. In the Journal of Sport and Health Science, Sun et al.³ reported data from the UK Biobank identifying the volume of LPA associated with reduced risks of all-cause mortality, cardiovascular disease (CVD) mortality, and CVD incidence, as well as reduced risks of cancer mortality and cancer incidence. Their cohort study included 69,492 adults, aged 43‒78 years. LPA was measured with a wrist-worn Axivity AX3 accelerometer for 7 days and scored as quartiles of minutes/week (min/week) and associated hours/day (h/day) of LPA (min/week (h/day) from lowest to highest: <1656 (<3.9), 1656 to <2090 (3.9–<5.0), 2090 to <2574 (5.0–<6.1), ≥2574 (≥6.1)). CVD incidence and mortality were obtained from primary care clinics, hospital admissions, and death records, respectively. A composite measure of incidence and mortality across all cancer types (except skin cancer) was obtained from cancer registry records. Descriptive variables were measured to control for potential covariation and confounding. The median follow-up period from study initiation to event observation was 8.04 years. Descriptive data were presented as mean ± SD, hazard ratios (HRs), and 95% confidence intervals (95%CIs) comparing the risk of being in the lowest LPA quartile (<3.9 h/day) vs. the highest 3 LPA quartiles. The risk of mortality and disease incidence was estimated using unadjusted and adjusted Cox proportional hazards models. In the fully adjusted model, the highest 3 quartiles of LPA min/week (3.9–≥6.1 h/day) were associated with a 25% to 18% reduction in all-cause mortality (HRs: 0.75‒0.82, 95%CI: 0.66‒0.93) and a 32% to 22% reduction in CVD mortality (HRs: 0.68‒0.78, 95%CI: 0.53‒0.98). A 23% to 17% reduction in cancer mortality was observed only for the 2 highest LPA min/week (5.0–≥6.1 h/day) quartiles (HRs: 0.77‒0.83, 95%CI: 0.65‒0.99). Risk reductions for CVD incidence and cancer incidence were lower and limited to the 2 highest LPA min/week quartiles for CVD incidence (HR = 0.92, 95%CI: 0.86‒0.98) and the highest LPA min/week (≥6.1 h/day) for cancer incidence (HR = 0.92, 95%CI: 0.85‒0.99). These results add to the evidence that engagement in LPA reduces mortality risk^1,2,4 and provide evidence of protection against CVD and cancer incidence. Inverse, non-linear dose‒response patterns were observed (vs. the referent 5th percentile LPA of 1114 min/week (2.65 h/day)) for the minimal and optimal times spent in LPA to reduce all-cause, CVD, and cancer mortality risks, as well as CVD and cancer incidence. LPA from 1506 to 1619 min/week (3.58‒3.85 h/day) was associated with a minimum risk of all-cause mortality, CVD and cancer mortality, and CVD incidence. The minimum dose for cancer incidence was 1848 min/week (4.4 h/day). The optimal dose to lower risks for all mortality types and CVD incidence risk ranged from 2404 to 2929 min/week (5.70‒6.97 h/day). There was no optimal dose to lower the risks of cancer incidence. Based on the doses associated with reduced risks of mortality and disease incidence, the authors concluded that engaging in LPA between ∼3.5 h/day and ∼6.0 h/day represents the minimal and optimal volume, respectively, to reduce these risks.

The results from Sun et al.³ provide additional evidence that sustained engagement in LPA reduces the risk of all-cause premature mortality and disease incidence by 18% to 25%. This is consistent with the evidence showing a 20% to 30% lowered risk of premature mortality and disease incidence from moderate- and vigorous-intensity physical activity (MVPA).⁵ The difference between engagement in LPA and MVPA is in the duration needed to confer protection. Sun et al.³ identified minimal and optimal durations of LPA ranging from <1656 to ≥2574 min/week (3.9‒6.1 h/day), whereas the World Health Organization’s guidelines call for 150‒300 min/week and 75‒150 min/week of MVPA, respectively, or a combination of the 2 intensities.⁶ These durations translate into a recommended 3.5 to >6 h/day for LPA and as little as 30 min/day for 5 days/week (moderate) to 30 min/day for 3 days/week (vigorous) for MVPA. Clearly, deriving mortality-reducing benefits from LPA, without engaging in MVPA, requires considerably more time spent moving and less time sitting during the day.

Few studies report LPA volumes associated with reduced mortality risk. Matthews et al.⁷ reported that adults aged ≥40 years enrolled in the National Health and Nutrition Examination Survey (NHANES) who accumulated 4.4 to 5.0 h/day LPA (vs. the referent 3 h/day) had a 21% to 23% lower risk of all-cause mortality (HRs: 0.79‒0.77, 95%CI: 0.70‒1.0). This finding is similar to the 18% to 25% reductions in all-cause mortality and LPA volume reported by Sun et al.³ In a meta-analysis of 8 studies, including 72.8% older women, with a mean age of 62.6 years, Ekelund et al.¹ identified 350 min/day (5.8 h/day) vs. the referent 28 min/day as the optimal LPA volume associated with a 34% to 56% reduced mortality (HRs: 0.44‒0.66, 95%CI: 0.34‒0.74). Ekelund et al.’s¹ LPA volume is consistent with the optimal volume of LPA to reduce mortality risk reported by Sun et al.³ (6.0 h/day). However, Ekelund et al.’s¹ HRs of 0.44‒0.66 reflect a considerably stronger risk reduction than reported by Sun et al.³ (HRs: 0.75‒0.82, 95%CI: 0.66‒0.93). Ekelund et al.¹ surmised that, in their meta-analysis, which included only studies that set accelerometer cut points at 101‒1950 counts per minute to classify LPA, the upper range of this cut point may have been too high for older adults, thereby classifying more moderate-intensity physical activity as LPA. For future studies, Ekelund et al.¹ suggested that accelerometer calibration studies be conducted with older adults to determine LPA cut points based on their percent maximal cardiorespiratory fitness (i.e., %VO_2max), instead of using LPA cut points determined for adults. This could improve the precision of identifying associations between LPA and mortality in this population.

Researchers have used subjective and objective measures of LPA to identify time spent in LPA throughout the day.^2,7,8 Subjective measures (e.g., self-report questionnaires and logs) are considered unreliable in research due to the difficulty of recalling unstructured past LPA activities.^1,9,10 Alternatively, objective measures, such as accelerometers, provide greater precision in recording movement intensity and duration across consecutive days and are considered the standard method for quantifying time spent in LPA.¹ As accelerometers are used primarily in research settings, non-researchers without access to them can instead estimate time spent in LPA by measuring the hours and minutes spent in different LPA types. The 2024 Compendium of Physical Activities identifies LPAs (and sedentary behaviors and MVPA) performed across 22 activity categories, including housework, home repair, lawn and garden, transportation, occupational, walking, sports and recreation, conditioning, and dancing activities.¹¹ Within the 1.6‒2.9 MET LPA intensity category, common activities such as household chores, childcare, light gardening, and walking can be timed to quantify time spent in LPA. For example, walking in the house requires 2.3 METs, and casual walking at 2.0‒2.4 miles per hour (3.2‒3.9 km/h) requires 2.3‒2.8 METs. Many household chores are classified as LPA (e.g., doing laundry, caring for animals, preparing meals, and light cleaning). These activities are often performed by women, especially older women, who engage in lower amounts of recommended MVPA, if any, than men and younger women.¹² In a subgroup analysis, Sun et al.³ observed that adults aged ≥60, females, persons engaging in <150 min/week MVPA, engaging in ≥3 h/day in screen time, and those with poorer self-reported health had the most protective benefits from LPA in all-cause and cause-specific mortality, CVD incidence, and cancer incidence compared with their demographic counterparts. These findings provide encouraging evidence of reduced mortality and health improvements (e.g., glycemic control) with LPA among older adults, adults with poorer health, women, and those who do not meet recommended MVPA amounts.

The potential impact of LPA on the health and longevity of older adults cannot be understated. Aging promotes a cascade of physiological changes, including sarcopenia and related functional impairments (e.g., decreased strength and power) that contribute to frailty and increased fall risk, as well as mitochondrial dysfunction that impairs metabolic processes and contributes to frailty.^13,14 Evidence suggests that increasing time spent in LPA can reduce systemic inflammation associated with sedentariness and obesity,¹⁵ improve glycemic control,¹⁶ and increase blood flow to the brain involved in motor skills and cognitive functioning.¹⁷ Johnson et al.¹⁸ reported that LPA was associated with improved executive functioning in older adults, a finding that is important for information processing and cognitive flexibility. LPA also enhances aspects of physical fitness associated with aging. For example, Twiddy et al.¹⁹ showed that higher amounts of LPA were significantly associated with a 28% higher odds of good balance (HR = 1.28, 95%CI: 1.15‒1.41) among adults aged ≥65 years compared with those with less LPA and that each 60-min increase in LPA was significantly associated with 19% higher odds of good static balance (HR = 1.19, 95%CI: 1.09‒1.31). Brown et al.²⁰ reported that a low-intensity exercise program favorably modified physical fitness measures (i.e., balance, strength, coordination, and reaction time) in frail older adults aged 83 ± 4 years. Additionally, Yang et al.¹⁴ reported that among robust, prefrail, and frail older adults aged 62.0 ± 7.8 years enrolled in the UK Biobank study, those in the highest tertile of LPA (∼>6 h/day) gained an additional ∼3.0 years of life at age 50 compared with those in the lowest tertile of LPA (∼<3 h/day). Collectively, the research studies show that daily LPA helps reduce systemic inflammation, maintain metabolic and muscle function, improve stability, reduce the risk of falls in older adults, and increase longevity. Achieving these important health benefits through LPA for 3.5‒6.0 h/day is feasible, especially if older adults incorporate walking, resistance exercises, and household chores that involve more movement and less sitting into their daily lives.

Sun et al.’s³ study advances understanding of the LPA volume needed to reduce the risk of all-cause, CVD, and cancer mortality, as well as the incidence of CVD and cancer. As CVD is the leading cause of death in men and women,²¹ the findings from this study reinforce the need for middle-aged and older adults to engage in at least 3.5 h/day of LPA and aim for 6.0 h/day to reduce their risk of premature mortality and enhance longevity, especially if they do not engage in MVPA. While these results pertain to a cohort of middle-aged and older men and women enrolled in the UK Biobank study, their study contributes to the accumulating evidence that LPA is beneficial for one’s health and reduces premature mortality. However, the feasibility of individuals engaging in daily LPA from 3.5 h to 6.0 h and the reproducibility of these results need to be established in additional studies and diverse populations before this volume of LPA can be adopted as a public health recommendation.

Authors’ contributions

BEA conceived the commentary, drafted, and edited the manuscript; HT and ZC helped draft and edit the manuscript. All authors have read and approved the final version of the manuscript, and agree with the order of presentation of the authors.

Declaration of competing interest

All authors declare that they have no competing interests. Given her role as Deputy Editor-in-Chief, BEA had no involvement in the peer review of this article and had no access to information regarding its peer review. Full responsibility for the editorial process for this article was delegated to another journal editor.