Seasonal Changes in Midlife Women'S Percentage Body Fat: A 1-Year Cohort Study.

Objective: The purpose of this longitudinal, observational study was to examine whether age and seasonal changes in sedentary activity (sedAct), moderate-to-vigorous physical activity (MVPA), and energy intake (EI) predict changes in body composition among midlife women. We hypothesized that reductions in MVPA and increases in sedAct and EI in winter, along with greater baseline age would predict increases in percentage body fat (%BF) across seasons.

Design: This study used a longitudinal, within-subjects design. Setting: This study took place in Grand Forks, North Dakota.

Participants: Participants included 52 midlife women (aged 40-60 years) who were observed over the course of one year.

Measurements: Percentage body fat measures were obtained via whole body Dual Energy X-ray absorptiometry. Participants were scanned once per season. We measured EI using the ASA24®. We used a GTX3 accelerometer to measure physical activity. Each season, participants wore the monitors for 7 days, 12 hours per day. All measures began in summer.

Results: Results of hierarchical multiple regression (MR) analyses showed that age increases (β = 0.310, p = 0.021) and summer-to-fall increases in EI (β = 0.427, p = 0.002) predicted seasonal increases in %BF (R2 = .36, F(5, 42)= 4.66, p = 0.02). Changes in MVPA and sedAct were not significant predictors. Repeated measures ANCOVA revealed that summer (M = 37.7263, 95% CI [35.8377, 39.6149]) to winter (M = 38.1463, 95% CI [36.1983, 40.0942]) increases in %BF are not reversed by spring (M = 37.8761, 95% CI [35.9365, 39.8157]).

Conclusions: To minimize increases in %BF and maintain health, midlife women, particularly older women, should be encouraged to pay extra attention to their diet in the fall months.