PAVEY, TOBY G.1; PEETERS, GEESKE1; BAUMAN, ADRIAN E.2; BROWN, WENDY J.1
The benefits of regular physical activity (PA) for health and mortality are irrefutable. PA has an inverse relationship with many health outcomes, including coronary heart disease, diabetes, cancers, and depression, and further with all-cause mortality (4,12,16,28). These relationships are based on epidemiological data, where PA is generally a self-reported measure of moderate and vigorous PA (MVPA). Given this evidence, many current PA guidelines recommend 30 min of at least moderate-intensity PA (MOPA) on most days of the week (150 min·wk−1) for general population health benefits (9,10). More recent guidelines from the USA and the UK recognize that because vigorous PA expends approximately twice the energy of MOPA, equivalent health benefits can also be attained from 75 min of vigorous activity (26,27). However, in several countries, including Australia and New Zealand, there is an additional recommendation to “If you can, also enjoy some regular, vigorous activity for extra health and fitness” (10,22).
There is some evidence to suggest that vigorous PA may provide additional physical and mental health benefits over those that result from moderate-intensity activity (24,25). However, it is unclear whether these additional benefits simply reflect the greater amount of activity that is usually accrued by those who do vigorous activity, as few studies have controlled for overall volume of activity (19).
Although women typically report less leisure time PA than men, in Australia, we have recently seen an increase in activity levels in middle-age women (45–55 yr), commensurate with more “free” time as children leave home and hours in paid work tend to decrease (6). Most of this increase in PA is attributable to walking, which is known to have demonstrable health benefits (13,15). Few women, however, seem to be taking up the recommendation of doing vigorous activity for extra health benefits; this could be important because metabolic changes around the time of menopause initiate an increase in the incidence of chronic disease (2).
The aim of this study was to assess whether vigorous PA has additional health benefits above those that accrue from MOPA (including walking) in middle-age women. We chose to use hypertension (HT) and depression as outcomes because these conditions are the most common physical and mental health outcomes, respectively, for primary care management in Australia (3). The approach was to compare the reduction in risk of developing HT and depressive symptoms (DS) for 12 yr in middle-age women who reported (a) only MOPA and (b) a combination of MVPA, after controlling for overall volume of activity.
The Australian Longitudinal Study on Women’s Health (ALSWH) is a prospective study of factors shaping the health and well-being of three cohorts of Australian women (born in 1973–1978, 1946–1951, and 1921–1926), recruited from the national Medicare health insurance database. The focus of this article is on the 1946–1951 cohort (14). Participants completed mailed surveys in 1996, 1998, 2001, 2004, 2007, and 2010 (surveys 1–6). At baseline, the women were largely representative of women age 45–50 yr in the Australian population (14). More details can be found at http://www.alswh.org.au. The study was approved by the Universities of Newcastle and Queensland Ethic Committees, and all participating women provided informed consent. As the PA questions in survey 1 differed from the other surveys, survey 2 (1998) was taken as baseline for the current study, with data also drawn from surveys 3, 4, 5, and 6. Figure 1 shows the response rates of participants for surveys 2 through 6. For all variables, data were retrieved from surveys 2 to 6 using the same methods, except where indicated.
The occurrence of HT was assessed by the question “In the past three years, have you been diagnosed with or treated for HT?” (yes or no). DS was assessed by the 10-item Center for Epidemiological Studies Depression Scale, with participants who scored 10 points or higher classified as having DS (1,20).
Main explanatory variable
PA scores were calculated using a modified version of the Active Australia survey, which has acceptable measurement properties for population surveys (5). Women were asked to report time spent walking briskly and time spent in moderate leisure activities (e.g., golf, recreational swimming, and gardening) in the last week (moderate). Women were also asked to report time spent in vigorous leisure activities (e.g., competitive sport, running, and aerobics) in the last week (vigorous). Using MET values of 3.33 for moderate activities and 6.66 for vigorous activities, total volume of PA was calculated as (min·wk−1 in moderate PA × 3.33) + (min·wk−1 in vigorous PA × 6.66). Total volume of PA was then categorized as follows: none, >0 to <250, 250 to <500, 500 to <1000, 1000 to <1500, 1500 to <2000, and >2000 MET·min·wk−1. A score of 500 MET·min·wk−1 is commensurate with meeting current PA guidelines. In addition, each woman was categorized as doing none (inactive), MOPA, or a combination of moderate and vigorous–intensity PA (MVPA), depending on which types of activities they reported. A vigorous only category was not created because <2% of women reported doing vigorous activity, without any walking or moderate-intensity activity.
Other explanatory variables
Sociodemographic variables, including age, area of residence, and marital status, were derived from survey 2 and categorized as shown in Table 1. The highest level of education was derived from survey 1.
Smoking status and alcohol consumption were assessed from survey 2 and categorized as shown in Table 1, with drinking categories based on the National Health and Medical Research Council (NHMRC) guidelines (17). Sitting time was measured at survey 3 (because it was not measured at survey 2) and categorized as 0 to 4, 4 to <8, 8 to <11, or ≥11 h·d−1, as per previous protocols (18).
Health-related variables were also derived from survey 2 data. They included the following: number of chronic conditions, categorized as none, one, two, or three or more, from a comprehensive list of conditions reported to have been diagnosed by a doctor in the previous 3 yr; and BMI (kg·m−2; calculated using self-reported weight and height), categorized as underweight, BMI < 18.5; normal weight, 18.5 ≤ BMI < 25; overweight, 25 ≤ BMI < 30; or obese, BMI ≥ 30 (30).
Differences between baseline covariates of the activity groups (inactive, MOPA, and MVPA) were analyzed using the chi-square test for categorical variables and ANOVA for continuous variables. The associations between PA intensities and occurrence of HT and DS were investigated using binary logistic generalized estimating equation models with a 3-yr time lag, in which PA scores measured at surveys 2–5 were matched with outcomes measured at surveys 3–6. Odds ratios (OR) were calculated for each category of PA by volume (i.e., 0, >0 to <250, 250 to <500 MET·min·wk−1, etc.) and intensity (i.e., inactive, moderate, and moderate plus vigorous), with the inactive group (0 MET·min·wk−1) as the reference category. Estimates for 0–250 and 250–500 MET·min·wk−1 PA categories had to be combined for the MVPA models because of low numbers in these two categories. The models presented were unadjusted and after adjustment for sociodemographic (age, education, marital status, and area of residence), behavioral (smoking, alcohol, and sitting), and chronic conditions covariates. BMI was added to the DS models, but not the HT models, because of the mediating properties of BMI in the association between PA and HT (11). Selection of covariates was based on previous ALSWH PA studies (7,8). All statistical analyses were conducted in SPSS (version 20; SPSS Inc., Chicago, IL). P values were based on two-sided tests and were considered statistically significant at P < 0.05.
Of the 12,338 women who returned survey 2 (baseline), 11,285 provided PA data (91.5%). Of these women, 2027 (18%) were classified as inactive (i.e., 0 MET·min·wk−1), 7365 (65.3%) as MOPA, and 1893 (16.8%) as MVPA. Sociodemographic, behavioral, and health data by PA intensity for the baseline sample are shown in Table 1. The mean age of the women in 1998 was 49.5 yr (range, 44.6–52.8 yr). Compared with women in the MOPA and MVPA groups, those who were inactive were more likely to have a low level of education, be a smoker, sit more, have more chronic conditions, and be obese (P < 0.01). Compared with women who were included in analyses, those who were excluded (due to missing data) were more likely at baseline to have low levels of education (P < 0.001), be “not partnered” (P < 0.001), be current smokers (P < 0.001), be nondrinkers (P < 0.001), and to report three or more chronic conditions (P < 0.001); they were also less likely to be classified as normal weight (P < 0.01). The proportion of women with missing data on any of the covariates was generally <1%. The exceptions were BMI and sitting time with 6.9% and 7.4% missing, respectively. Given the low rate of missing covariate data, we do not think this would have influenced the results. Descriptive PA data (mean MET·minutes per week and PA frequency per week) at each survey are shown in Table 2.
The relationships between PA volume and OR for HT and DS are shown in Figures 2 and 3, respectively. Compared with the inactive women, odds for HT declined with increasing PA volume. This decline was slightly but not significantly greater in the MVPA group than that in the MOPA group. At PA levels >2000 MET·min·wk−1, the OR for HT was 0.24 lower in the MVPA (0.56; 0.49–0.64) than that in the MOPA group (0.80, 95% confidence interval [CI] = 0.68–0.91). Adjustment for the covariates resulted in only slight attenuation of these OR values (see Table 3).
For DS, the OR values declined more markedly with increasing PA volume (than that for HT; see Fig. 2). At PA volumes higher than 500 MET·min·wk−1, OR values were 0.06–0.15 lower in the MVPA group than that in the MOPA group, but only statistically significantly different at the highest PA volume. Again, adjustment for covariates changed the results only slightly (see Table 3).
The aim of this study was to assess whether vigorous PA has additional health benefits (in terms of reduced risk of HT and DS) above those that accrue from MOPA (including walking) in middle-age women. The results suggest that inclusion of some vigorous activity results in greater reductions in the risk of both these conditions than moderate-intensity activity alone. However, the differences were small and only reached statistical significance at the highest volume of weekly activity.
Our results lend some support to previous reviews, which have concluded that MOPA provides protection against depression and cardiovascular risk, but that vigorous-intensity PA provides greater protection (21,23–25). Our adjusted results suggest that at 500–1000 MET·min·wk−1 level (meeting guidelines), there is an 18% reduction (OR = 0.82, 95% CI = 0.75–0.91) in risk of HT for MOPA but a 27% reduction (OR = 0.73, 95% CI = 0.62–0.86) in risk in those who reported MVPA compared with the risk in the inactive referent group. Similarly, at the same PA level, there is a 32% reduction (OR = 0.68, 95% CI = 0.61–0.75) in risk of DS for MOPA and a 42% reduction (OR = 0.58, 95% CI = 0.49–0.70) for MVPA, compared with the risk in the inactive referent group. However, these differences between the two intensity groups (for both HT and DS) were only statistically significant for the highest volume of PA. Therefore, although women who reported both moderate-intensity and vigorous-intensity activity seemed to have slightly greater risk reduction for both HT and DS than those who only reported moderate-intensity activity, it cannot be confidently concluded that the addition of vigorous-intensity PA confers greater benefit, except at the very highest levels of activity.
It should be noted that our study differs from most previous studies in this field because we could not include a “vigorous only” group. This was because most of the participants (65%, in this representative population-based cohort) typically accumulated their PA as moderate-intensity (including walking), whereas only 17% reported moderate (including walking) plus vigorous-intensity PA. Very few women (<2%) reported only vigorous PA. One study that has compared the effects of walking and vigorous exercise for the prevention of cardiovascular events in middle-age women used data from the Women’s Health Initiative Observational Study. The researchers found that women who met PA guidelines via either brisk walking or vigorous exercise had a 30% risk reduction in cardiovascular event incidence compared with women who reported no activity (15). In line with this, our results also show that MOPA (including walking) alone provides substantial health benefits for middle-age women.
Our results support the continued promotion of MOPA for protection against HT and DS, which are the most common reasons for a primary medical care visit by middle-age women. Although the results lend support to the notion in the current Australian PA guidelines, which suggests that vigorous-intensity PA may confer additional health benefits (10), the magnitude of the additional benefit is small for these two health outcomes. Importantly, the shape of the dose–response relationship suggests that volumes of PA below those currently recommended (500 MET·min·wk−1) also offer some protection against HT and DS. A recent article based on data from our older ALSWH cohort, and a cohort of older men in Western Australia, also showed that levels of PA lower than those currently recommended for health benefits are protective against mortality in older people (8). Nonetheless, optimal benefit seems to be in the 500- to 1000-MET·min·wk−1 range, with or without vigorous activity. This is in line with current international PA guidelines (27).
The strengths of this study include the large representative population-based sample, long-term follow-up, and inclusion of many confounding variables. However, the limitations of self-reported measures, for both the explanatory and outcome measures, should be acknowledged. We chose to focus on the occurrence of each health outcome at each survey because DS may come and go over time and because women who report HT at one survey may not report it at the next survey, if they perceive they no longer have the problem because it is controlled by medication. We did examine the relationships between PA and incidence of these two problems, but this requires that data are censored once women first report the problem, resulting in smaller cell sizes and wide CI for the risk estimates. The magnitude of the risk reductions was reduced, but the results for the comparison of MOPA and MVPA did not change (data not shown). In common with all prospective studies, attrition rates varied between study baseline (survey 2) and follow-ups (ranging from 3% to 10%). As women remaining in the study are likely to be more healthy and resilient, and because there were also sociodemographic differences between those whose data were included and excluded, the reported risk reductions are likely to be underestimated.
In conclusion, risks of HT and DS for 12 yr were slightly lower for any given volume (or dose) of PA when some vigorous-intensity activity was included than when only moderate and walking activities were reported. However, the additional benefit was small (a further risk reduction of approximately 0.1), and the difference in risk for women who reported MOPA and MVPA was only statistically significantly different at the highest volumes of PA.
The ALSWH, which was conceived and developed by a group of interdisciplinary researchers at the Universities of Newcastle and Queensland, is funded by the Australian Government Department of Health and Ageing. The funding source had no involvement in the research presented in this article.
This work was supported by the NHMRC (program grant no. 301200) at the University of Queensland, School of Human Movement Studies, for Dr. Pavey and Dr. Peeters. Dr. Peeters was also supported by the NHMRC Centre of Research Excellence in Women’s Health (grant no. APP1000986) at the University of Queensland, School of Population Health.
There are no conflicts of interest.
The results of the present study do not constitute endorsement by the American College of Sports Medicine.
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