Daily steps and all-cause mortality: a meta-analysis of 15 international cohorts.

BACKGROUND: Although 10 000 steps per day is widely promoted to have health benefits, there is little evidence to support this recommendation. We aimed to determine the association between number of steps per day and stepping rate with all-cause mortality. METHODS: In this meta-analysis, we identified studies investigating the effect of daily step count on all-cause mortality in adults (aged ≥18 years), via a previously published systematic review and expert knowledge of the field. We asked participating study investigators to process their participant-level data following a standardised protocol. The primary outcome was all-cause mortality collected from death certificates and country registries. We analysed the dose-response association of steps per day and stepping rate with all-cause mortality. We did Cox proportional hazards regression analyses using study-specific quartiles of steps per day and calculated hazard ratios (HRs) with inverse-variance weighted random effects models. FINDINGS: We identified 15 studies, of which seven were published and eight were unpublished, with study start dates between 1999 and 2018. The total sample included 47 471 adults, among whom there were 3013 deaths (10·1 per 1000 participant-years) over a median follow-up of 7·1 years ([IQR 4·3-9·9]; total sum of follow-up across studies was 297 837 person-years). Quartile median steps per day were 3553 for quartile 1, 5801 for quartile 2, 7842 for quartile 3, and 10 901 for quartile 4. Compared with the lowest quartile, the adjusted HR for all-cause mortality was 0·60 (95% CI 0·51-0·71) for quartile 2, 0·55 (0·49-0·62) for quartile 3, and 0·47 (0·39-0·57) for quartile 4. Restricted cubic splines showed progressively decreasing risk of mortality among adults aged 60 years and older with increasing number of steps per day until 6000-8000 steps per day and among adults younger than 60 years until 8000-10 000 steps per day. Adjusting for number of steps per day, comparing quartile 1 with quartile 4, the association between higher stepping rates and mortality was attenuated but remained significant for a peak of 30 min (HR 0·67 [95% CI 0·56-0·83]) and a peak of 60 min (0·67 [0·50-0·90]), but not significant for time (min per day) spent walking at 40 steps per min or faster (1·12 [0·96-1·32]) and 100 steps per min or faster (0·86 [0·58-1·28]). INTERPRETATION: Taking more steps per day was associated with a progressively lower risk of all-cause mortality, up to a level that varied by age. The findings from this meta-analysis can be used to inform step guidelines for public health promotion of physical activity. FUNDING: US Centers for Disease Control and Prevention.

APOE genotype and cardio-respiratory fitness interact to determine adiposity in 8-year-old children from the Tasmanian Infant Health Survey.

APOE plays a well established role in lipid metabolism. Animal model evidence suggests APOE may also be associated with adiposity, but this has not been thoroughly investigated in humans. We measured adiposity (BMI, truncal fat mass, waist circumference), physical activity (PA), cardiorespiratory fitness and APOE genotype (E2, E3, E4) in 292 8-year-old children from the Tasmanian Infant Health Survey (TIHS), an Australian population-based prospective birth cohort. Our aims were to examine the association of APOE with child adiposity, and to examine the interplay between this association and other measured factors. We found that APOE was associated with child lipid profiles. APOE was also associated with child adiposity measures. The association was E4 allele-specific, with adiposity lower in the E4-containing group (BMI: Mean difference -0.90 kg/m²; 95% confidence intervals (CI) -1.51, -0.28; p = 0.004). The association of APOE4 with lower BMI differed by fitness status (difference in effect p = 0.002), and was more evident among the less fit (mean difference -1.78 kg/m²; 95% CI -2.74, -0.83; p<0.001). Additionally, associations between BMI and lipids were only apparent in those of lower fitness who did not carry APOE4. Similar overall findings were observed when truncal fat mass and waist circumference were used as alternative adiposity measures. APOE4 and cardiorespitatory fitness could interact to influence child adiposity. In studies addressing the genetic determinants of childhood obesity, the context of child fitness should also be taken into account.

Practical considerations when using pedometers to assess physical activity in population studies: lessons from the Burnie Take Heart Study.

The aim of this study was to summarize both practical and methodological issues in using pedometers to assess physical activity in a large epidemiologic study. As part of a population-based survey of cardiovascular disease risk factors, physical activity was assessed using pedometers and activity diaries in 775 men and women ages 25-64 years who were residents of Burnie, Tasmania, 1998-99. Common data problems were classified by type. The frequency of each problem and the methods used to identify it are reported along with strategies to correct or prevent each problem type. Pedometer data from 15 (1.9%) participants could not be used due to errors in completing the pedometer protocol. Among 760 participants with usable data, the median number of steps was 9,729 for men and 10,388 for women. Pedometer steps per day were modestly correlated (r = .20, p < .0001) with the duration of pedometer wear, which ranged from 4.50 to 21.75 hr. Adjustment for wear time, however, did not alter observed correlations between pedometer steps and cardiovascular risk factors. The authors conclude that pedometers can be used in large population studies with a relatively low frequency of data errors. However guidelines for consistent data collection and interpretation are needed.

Parental smoking and infant respiratory infection: how important is not smoking in the same room with the baby?

OBJECTIVES: We sought to quantify the effect of good smoking hygiene on infant risk of respiratory tract infection in the first 12 months of life. METHODS: A cohort of 4486 infants in Tasmania, Australia, was followed from birth to 12 months of age for hospitalization with respiratory infection. Case ascertainment was 98.2%. RESULTS: Relative to the infants of mothers who smoked postpartum but never in the same room with their infants, risk of hospitalization was 56% (95% confidence interval [CI] = 13%, 119%) higher if the mother smoked in the same room with the infant, 73% (95% CI = 18%, 157%) higher if the mother smoked when holding the infant, and 95% (95% CI = 28%, 298%) higher if the mother smoked while feeding the infant. CONCLUSIONS: Parents who smoke should not smoke with their infants present in the same room.