The authors have declared that no competing interests exist.
Conceived and designed the experiments: AH JLM FG KS PS OSM EP PS. Analyzed the data: JLM. Wrote the paper: AH.
To investigate if persons with high physical activity at work have the same benefits from leisure time physical activity as persons with sedentary work.
In the Copenhagen City Heart Study, a prospective cohort of 7,411 males and 8,916 females aged 25–66 years without known cardiovascular disease at entry in 1976–78, 1981–83, 1991–94, or 2001–03, the authors analyzed with sex-stratified multivariate Cox proportional hazards regression the association between leisure time physical activity and cardiovascular and all-cause mortality among individuals with different levels of occupational physical activity.
During a median follow-up of 22.4 years, 4,003 individuals died from cardiovascular disease and 8,935 from all-causes. Irrespective of level of occupational physical activity, a consistently lower risk with increasing leisure time physical activity was found for both cardiovascular and all-cause mortality among both men and women. Compared to low leisure time physical activity, the survival benefit ranged from 1.5–3.6 years for moderate and 2.6–4.7 years for high leisure time physical activity among the different levels of occupational physical activity.
Public campaigns and initiatives for increasing physical activity in the working population should target everybody, irrespective of physical activity at work.
A sedentary lifestyle is an established risk factor for cardiovascular disease and mortality
Even today a considerable proportion of work active people have physically demanding jobs
Because of the negative cardiovascular and metabolic effects of excessive sedentary time per day
Accordingly, we investigated the preventive effect and survival benefit of leisure time physical activity on cardiovascular and all-cause mortality in the large Danish prospective cardiovascular epidemiological study – the Copenhagen City Heart Study.
The Copenhagen City Heart Study is a prospective population study in which a random sample of the population living in an area of Copenhagen is invited to participate at regular intervals. Details of the enrolment and examination are described elsewhere
In short, 14,223 persons (response rate 74%) participated in the first examination in 1976–78. In 1981–83, 1991–94, and 2001–03, these participants were re-examined and new, primarily young subjects were enrolled (see
The entire study sample consisted of persons participating in at least one of the four examinations (i.e. some persons participated in multiple examinations) in the Copenhagen City Heart Study who were free of previous cardiovascular disease (CVD) at their first examination in the study.
The median duration of follow-up was 22.4 years (range 0.01–35.3). Cardiovascular risk factors were assessed at each of the four examinations using the same standardised and validated methods as previously described in detail
The Committee of Biomedical Research Ethics for the Capital region in Denmark approved the study (H-KF-01-144/01). All data was de-identified and analyzed anonymously. The participants provided written consent to participate in the study. This consent procedure was approved by the ethics committee.
A single question with four answer options was applied for measuring occupational physical activity: ‘Which description most precisely covers your pattern of physical activity at work?
You are mainly sedentary and do not walk much around at your workplace.
You walk around quite a bit at your workplace but do not have to carry heavy items.
Most of the time you walk, and you often have to walk up stairs and lift various items. Examples include mail delivery and construction work. [Score 3].
You have heavy physical work. You carry heavy burdens and carry out physically strenuous work.
Because of very few females in the highest category of occupational physical activity, the variable was categorised into: score 1 = “low”, score 2 = “moderate”, and score 3–4 = “high”. For males, the four categories of occupational physical activity were applied and termed: score 1 = “low”, score 2 = “moderate”, score 3 = “high”, and score 4 = “very high”.
A single question with four answer options was applied for measuring leisure time physical activity:
‘Which description most precisely covers your pattern of physical activity during leisure time?
Being almost entirely sedentary (e.g., reading, watching television or movies, engaging in light physical activity such as walking or biking for less than 2 hours per week). [Score 1].
Engaging in light physical activity for 2–4 hours per week. [Score 2].
Engaging in light physical activity for more than 4 hours per week or more vigorous activity for 2–4 hours per week (e.g., brisk walking, fast biking, heavy gardening, sports that cause perspiration or exhaustion). [Score 3].
Engaging in highly vigorous physical activity for more than 4 hours per week or regular heavy exercise or competitive sports several times per week. [Score 4]’.
Because of very few females and males in the highest category of leisure time physical activity, the variable was categorised into: score 1 = “low”, score 2 = “moderate”, and score 3–4 = “high”.
Potentially confounding factors for the association between occupational and leisure time physical activity and cardiovascular and all-cause mortality were measured as follows:
Information on smoking habits was self-reported based on a single-item question, and the study participants were categorized as never smokers, ex-smokers, and current smokers of 1–14, and ≥15 cigarettes per day.
Information on alcohol consumption was self-reported, and the study participants were categorized in the statistical analyses as abstainers, or monthly, weekly, or daily consumers.
Household income was self-reported based on average income per month within the last year and categorized as low, medium, and high.
Diabetes was self-reported or a non-fasting blood glucose ≥11.1. Treatment for hypertension was self-reported, and categorized as yes/no.
Systolic blood pressure was measured in a sitting position after 5 minutes of rest, and applied as a continuous variable in the statistical analysis.
Body mass index (BMI) was calculated as measured weight (kg) divided by measured height squared (m2), and categorized for the statistical analyses as underweight (<18.5), normal weight (18.5–24.9), overweight (25–29.9) and obese (> = 30). Cholesterol was measured non-fasting in millmoles per litre.
Follow-up was carried out by data linkage to national registers. Deaths were obtained until June 2011 from The Civil Registration System and causes of death from The National Register of Causes of Death until January 2010. Cardiovascular death was defined as ICD-8: 390–458 and ICD-10: I00–I99.
For the univariate analyses of demographics, lifestyle, and clinical factors (
Sex | Males | Females | |||||||
Occupational physical activity | Low n = 2,146 | Moderate n = 1,911 | High n = 1,738 | Very High n = 905 | Low n = 2,309 | Moderate n = 3,473 | High n = 2,316 | ||
Age, mean (SD) | 44.8 (12.7) | 47.6 (11.4) | 47.4 (11.1) | 46.7 (10.8) | <0.001 | 45.2 (12.5) | 49.5 (11.0) | 44.1 (11.1) | <0.001 |
BMI, mean (SD) | 25.0 (3.6) | 25.4 (3.6) | 25.7 (3.6) | 26.6 (3.9) | <0.001 | 23.7 (4.1) | 24.4 (4.3) | 24.2 (4.3) | <0.001 |
Current smokers, % | 60.0 | 66.6 | 69.9 | 73.2 | <0.001 | 56.8 | 55.5 | 61.6 | <0.001 |
Consuming ≥1 unit alcohol a day, % | 29.8 | 34.8 | 41.6 | 53.2 | <0.001 | 11.5 | 11.1 | 9.3 | 0.026 |
Low leisure time physical activity, % | 17.4 | 13.8 | 15.2 | 19.9 | <0.001 | 18.2 | 15.9 | 12.5 | <0.001 |
Cholesterol, mean (SD) | 5.7 (1.2) | 5.8 (1.2) | 5.8 (1.2) | 5.9 (1.2) | <0.001 | 5.8 (1.4) | 6.1 (1.3) | 5.8 (1.2) | <0.001 |
Systolic blood pressure, mean (SD) | 135.0 (18.8) | 136.7 (19.3) | 135.8 (18.8) | 136.2 (17.6) | 0.030 | 127.6 (20.1) | 131.6 (21.0) | 126.2 (19.1) | <0.001 |
Blood pressure medication, % | 3.9 | 3.6 | 3.1 | 2.4 | 0.172 | 4.3 | 5.2 | 3.3 | 0.002 |
Diabetes, % | 2.6 | 2.8 | 2.7 | 3.2 | 0.837 | 1.2 | 1.5 | 1.3 | 0.513 |
High household income, % | 38.9 | 29.3 | 17.1 | 15.2 | <0.001 | 26.0 | 23.4 | 21.8 | 0.005 |
<8 years of school education, % | 18.8 | 33.1 | 47.4 | 58.2 | <0.001 | 20.9 | 41.9 | 41.5 | <0.001 |
With sex-specific multi-adjusted Cox proportional hazards regression models with time-dependent covariates and age as the underlying time scale and delayed entry (optimizing adjustment for age), the associations between leisure time physical activity and the outcomes were studied within each category of occupational physical activity. The predictive variables and covariates were attained from the examination of entry of each participant, and thereafter updated at each of the following examinations. All adjusted models included the covariates age, calendar time, smoking, alcohol consumption, BMI, occupational or leisure time physical activity, systolic blood pressure, diabetes, blood pressure medication, and household income.
Moreover, adjusted sex-specific Cox proportional hazards regression analyses were performed with a multiplicative interaction term between occupational and leisure time activity. Further, the survival benefit was calculated by integrating the survival function estimated in the Cox models. The survival benefit was calculated for a healthy average person (mean value of blood pressure, cholesterol, BMI, household income, and a never smoker, without diabetes and not taking blood pressure medication, and consuming alcohol on a monthly basis).
The assumption of proportionality in the Cox regression models was tested with the Lin, Wei, and Ying score process test
P-values below 0.05 were considered statistically significant. Statistical analyses were performed with R version 2.13.1.
During a median follow-up of 22.4 years (range 0.01–35.3), 4,003 (males: 2,087) died from cardiovascular disease and 8,935 (males: 4,401) from all-causes.
Among females, those with a high occupational physical activity level were more frequently current smokers, were less physically active in their leisure time and more often had less than 8 years of school education compared to females with a low occupational physical activity level.
Adjusted for age, calendar time, BMI, smoking, alcohol consumption, cholesterol, systolic blood pressure, blood pressure medication, diabetes and household income, survival benefit was calculated for a healthy average person (mean value of BMI, systolic blood pressure, cholesterol, household income, and a never smoker, without diabetes and not taking blood pressure medication, and consuming alcohol on a monthly basis) by integrating the survival function estimated in the Cox models.
Physical activity at work | Leisure time physical activity | All-cause mortality | Cardiovascular mortality | ||||||
Cases | HR | 95% CI | p-value | Cases | HR | 95% CI | p-value | ||
|
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Low | Low | 348 | 1.64 | 1.41, 1.89 | p<0.001 | 182 | 1.54 | 1.25, 1.88 | p<0.001 |
Low | Moderate | 656 | 1.13 | 1.00-1.28 | p = 0.045 | 311 | 0.98 | 0.83, 1.16 | p = 0.838 |
Low | High | 433 | 1.00 | Reference | 236 | 1.00 | Reference | ||
Moderate | Low | 215 | 1.60 | 1.36, 1.89 | p<0.001 | 114 | 1.59 | 1.25, 2.01 | p<0.001 |
Moderate | Moderate | 603 | 1.19 | 1.05, 1.35 | p = 0.006 | 266 | 0.98 | 0.82, 1.17 | p = 0.833 |
Moderate | High | 379 | 1.01 | 0.88, 1.16 | p = 0.879 | 181 | 0.91 | 0.75, 1.11 | p = 0.340 |
High | Low | 166 | 1.48 | 1.22, 1.79 | p<0.001 | 70 | 1.15 | 0.87, 1.52 | p = 0.317 |
High | Moderate | 483 | 1.21 | 1.06, 1.38 | p = 0.004 | 221 | 1.07 | 0.89, 1.28 | p = 0.500 |
High | High | 373 | 1.07 | 0.93, 1.23 | p = 0.334 | 184 | 1.01 | 0.83, 1.23 | p = 0.903 |
Very high | Low | 84 | 1.65 | 1.30, 2.09 | p<0.001 | 36 | 1.36 | 0.95, 1.95 | p = 0.093 |
Very high | Moderate | 161 | 1.33 | 1.10, 1.62 | p = 0.004 | 76 | 1.24 | 0.95, 1.63 | p = 0.110 |
Very high | High | 160 | 1.20 | 1.00, 1.45 | p = 0.055 | 68 | 1.01 | 0.77, 1.32 | p = 0.938 |
|
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Low | Low | 386 | 1.58 | 1.34, 1.87 | p<0.001 | 181 | 1.59 | 1.22, 2.07 | p<0.001 |
Low | Moderate | 699 | 1.22 | 1.05, 1.41 | p = 0.007 | 293 | 1.20 | 0.95, 1.51 | p = 0.133 |
Low | High | 219 | 1.00 | Reference | 94 | 1.00 | Reference | ||
Moderate | Low | 448 | 1.51 | 1.29, 1.78 | p<0.001 | 217 | 1.63 | 1.27, 2.10 | p<0.001 |
Moderate | Moderate | 1295 | 1.08 | 0.94, 1.24 | p = 0.268 | 551 | 1.03 | 0.83, 1.29 | p = 0.781 |
Moderate | High | 492 | 1.04 | 0.89, 1.21 | p = 0.642 | 184 | 0.89 | 0.69, 1.13 | p = 0.335 |
High | Low | 131 | 1.52 | 1.23, 1.89 | p<0.001 | 59 | 1.72 | 1.24, 2.40 | p = 0.001 |
High | Moderate | 416 | 1.24 | 1.06, 1.46 | p = 0.008 | 160 | 1.25 | 0.96, 1.62 | p = 0.095 |
High | High | 210 | 1.07 | 0.89, 1.29 | p = 0.489 | 75 | 1.03 | 0.76, 1.39 | p = 0.870 |
To further illustrate the impact of leisure time physical activity on longevity within different occupational physical activity groups,
The results of this study support that leisure time physical activity is associated with a reduced risk of cardiovascular as well as all-cause mortality among men and women independent of their level of occupational physical activity.
Overall, moderate leisure time physical activity was associated with a reduction in risk of cardiovascular and all-cause mortality ranging from 6 to 38% depending on level of occupational physical activity. An even more pronounced reduction in risk, ranging from 11 to 44%, was found among individuals with a high leisure time physical activity level. Moreover, the increase in life expectancy for both sex ranged from 1.5–3.6 years for moderate and 2.6–4.7 years for high leisure time physical activity among the different levels of occupational physical activity.
As shown in
Because of the well documented increased risk for CVD from sedentary behaviour
In another recent publication from the Copenhagen City Heart Study, men who were sedentary in leisure time had no benefit from being exposed to physically demanding work
As shown in
The main strengths of the present study are the relatively long follow-up time, control for socioeconomic factors, repeated measures of exposure and risk factors, several objective measures of risk factors for cardiovascular disease, and inclusion of both males and females. A limitation of the study is lacking control for psychosocial work factors. However, previous studies have shown that control for psychosocial factors have minimal influence on the association between occupational physical activity and cardiovascular disease and mortality
Among both men and women leisure time physical activity was inversely associated with risk of CVD mortality and all-cause mortality independent of the level of occupational physical activity. The implications of the findings in this study may be that future public campaigns and initiatives for increasing physical activity in the working population should target everybody, irrespective of their level of occupational physical activity.