Marco Mario Ferrario describes for SIIC his article published in Heart 104(14):1165-1172, July 2018

Milán, Italia (special for SIIC)
Physical activity (PA) is an important modifiable protective factor for the development of CVD. Since 2008 the American Heart Association (AHA), in its guidelines since 2008 recommends adults to perform at least 150 min per week of moderate-intensity activity or 75 min per week of vigorous-intensity activity or 150 min per week of moderate and vigorous-intensity activities combined1. In AHA guidelines no distinctions are made between occupational physical activity (OPA), leisure-time physical activity (LTPA) or sport; and previous studies on the relationship between OPA and CVD has shown contradictory results.

The aim of our study was to investigate the independent associations and the interactions between OPA and SpPA and the incidence of total cardiovascular and coronary events in cohorts of North Italian working men.

Our study is a pooled analysis of three population-based and one factory-based prospective cohorts of 3574 men, aged 25 to 64 years, working as salaried employees and CVD free at baseline2,3. PA was assessed with the Baecke Questionnaire4 which investigates both occupational (8 items) and sport (4 items) PA domains. Three OPA categories were obtained dividing into tertiles the original OPA score; while three SpPA categories were obtained from "minutes per week" of moderate or vigorous activity based on a method previously proposed5. Cardiovascular risk factors (body mass index, total and HDL cholesterol, blood pressure, current smoking, fasting glucose and alcohol intake) were also measured at baseline, using the standardized MONICA Project procedures2,3. To estimate the association of OPA and SpPA categories with the incidence of CVD, we used Cox proportional hazards models adjusted for age, cohort type and educational level (first model), plus multiple CVD risk factors (second model). Finally, we explored the protective role of SpPA among workers engaged in different levels of OPA by adding relevant SpPA-OPA interaction terms in age and CVD risk factor-adjusted Cox regression models, and formally testing the presence of additive interaction on the log(HR) scale with a Wald χ2 test.

Among the 3574 men, in a median follow-up time of 14 years, 174 first fatal and non-fatal CVD events (135 CHD) occurred. Low and high OPA categories showed higher CHD risks compared to the intermediate OPA category but only for low OPA category the risk excess was statistically significant (HR: 1.61 with 95% CI 1.02 to 2.52 in multiple-risk factors adjusted model). The increased CVD and CHD risk in low OPA category start to reveal after 3"5 years of follow-up (Kaplan-Meier survival curves).

We found a decreased risk in recommended and intermediate SpPA categories in comparison to poor SpPA: the age-adjusted CVD risk reduction was of 32% (HR: 0.68 with 95% CI 0.46 to 0.98) for the intermediate and recommended SpPA categories combined. The adjustments for CVD risk factors reduced the associations, due to the mediation effects of most risk factors. When we tested SpPA-OPA interaction on CHD and CVD risks, we found that the prominent protective effect of recommended and intermediate SpPA was restricted to low OPA workers (HR: 0.45 with 95% CI 0.24 to 0.87 and HR: 0.45 with 95% CI 0.25 to 0.82 for CHD and CVD respectively) while this effect disappeared in the intermediate OPA category, and even reversed in the high OPA category (HR:1.84 with 95% CI 0.88 to 3.87 and HR: 1.66 with 95% CI 0.87 to 3.14 for CHD and CVD, respectively).

In our working male population from North Italy, we found increased CHD incidence rates among workers with low and high levels of OPA. These results are similar to those of other studies6,7 and seem to confirm the "OPA health paradox8" suggesting the detrimental effect on CVD outcomes of high levels of OPA. On the other hand, other studies have shown opposite results9-11. Reasons for these discrepancies may be due to the different methods adopted for the assessment of OPA, and also to the differences in the length of follow-up.

Our study then confirms the protective role of SpPA on CVD and CHD risk shown by most studies12,13, prominent among sedentary workers (risk reduction of 55%), and an opposite relationship for workers with a higher level of OPA with increased risk up to 66% for CVD and 84% for CHD. These findings suggest that the strongest effect of SpPA is concentrated in sedentary workers while it can be less beneficial, or even harmful, in people performing heavy physical working tasks. This may be due to an overloading of the cardiovascular system caused by the jointly high physical activity at work and in leisure time which, over years and with insufficient recovery, can lead to the development of CVD14.

Our study presents some limitations: PA was calculated using a self-administered questionnaire, once at the baseline so we can assume some misclassification bias due to changes in PA habits over time. Another limitation is the focus on men and salaried workers only. Finally, our data do not allow to further investigate the separate effects of walking and lifting at work on the CVD risk, as the large majority of high OPA workers (67%) reported concomitant exposures.

In conclusion, our study conducted on North Italian male workers suggests a prominent protective effect of AHA recommended an intermediate sport PA levels on CVD among sedentary workers and an opposite effect in people involved in physically demanding work tasks. Due to the increasing number of sedentary workers in post-industrialized countries, interventions to promote SpPA in working populations could be an important factor to reduce the burden of CVD. In addition, future CVD prevention guidelines should consider tailoring the recommendations on the amount of PA during leisure time to the levels of PA at work.