Factors associated to leisure-time sedentary lifestyle in adults of 1982 birth cohort , Pelotas , Southern Brazil

OBJECTIVE: To assess factors associated to leisure-time physical activity and sedentary lifestyle. METHODS: Prospective cohort study of people born in 1982 in the city of Pelotas, southern Brazil. Data were collected at birth and during in a visit in 2004-5 when 77.4% of the cohort were evaluated, making a total of 4,297 people studied. Information about leisure-time physical activity was collected using the International Physical Activity Questionnaire. Sedentary people were defi ned as those with weekly physical activity below 150 minutes. The following independent variables were studied: gender, skin color, birth weight, family income at birth and income change between birth and 23 years of age. Poisson’s regression with robust adjustment of variance was used for the assessment of risk factors of sedentary lifestyle. RESULTS: Men reported 334 min of weekly leisure-time physical activity compared to 112 min among women. The prevalence of sedentary lifestyle was 80.6% in women and 49.2% in men. Scores of physical activity increased as income at birth increased. Those who were currently poor or who became poor during adult life were more sedentary. CONCLUSIONS: Leisure-time sedentary lifestyle in young adults was high especially among women. Physical activity during leisure time is determined by current socioeconomic conditions. DESCRIPTORS: Leisure Activities. Exercise. Socioeconomic Factors. Cohort Studies. Brazil.


INTRODUCTION
Physical activity is vital for the prevention and treatment of conditions such as hypertension, ischemic heart disease, diabetes, depression, and some cancers, among others. 5But the prevalence of sedentary lifestyle in the general population is high 11 especially during leisure time. 1,7,20The comparability of prevalences of sedentary lifestyle in different studies is hindered due to the application of widely varied instruments and defi nition criteria. 16Recent studies have suggested that exposures during pregnancy or in the fi rst years of life may be associated to the development of chronic diseases. 3,15,19However, few studies have evaluated whether physical activity can be programmed by exposures in the fi rst years of life.
Hallal et al 13 found that the prevalence of sedentary lifestyle in children aged ten to 12 was higher among those with higher family income at birth and higher maternal schooling.They did not fi nd an association between sedentary lifestyle and birth weight or weight gain in the fi rst year of life. 13Bearing in mind the relevance of identifying determinants of sedentary lifestyle, the objective of the present study was to assess factors associated to leisure-time physical activity and sedentary lifestyle.

METHODS
Prospective cohort study of people born in 1982 carried out in the city of Pelotas, southern Brazil.The cohort methods are detailed elsewhere. 2,23,24In the follow-up period during 2004-5, leisure-time physical activity was assessed using the International Physical Activity Questionnaire (IPAQ, long version). 6Trained interviewers administered the questionnaire to collect information on different health-related aspects such as weekly frequency of physical activity and average duration of walking and other physical activity, either moderate or vigorous, during a regular week.
Weekly scores of physical activity were estimated by the sum of time reported of walking, moderate physical activity (e.g., recreational sports and biking) and the time spent on vigorous activities multiplied by two (competition sports and running).Those showing a weekly score of less than 150 minutes were considered sedentary based on current recommendations of physical activity. 10,14e mothers of the children studied were interviewed right after delivery and information on family income and birth weight, among others, was collected.Based on family income during 2004-5, it was possible to estimate income change over the study period.The skin color was self-referred by interviewees in 2004-5.
The sample was described as proportions and means.Bivariate analysis was performed using chi-square test to assess heterogeneity and linear trend of ordinal variables.Poisson's regression with robust adjustment for variance was used to assess risk factors of sedentary lifestyle. 4In the adjusted analysis, the variables at the fi rst level -skin color and family income in 1982 -were adjusted for and included in the model if p<0.2.Income change was adjusted for skin color and birth weight was adjusted for the variables at the fi rst level.
Verbal informed consent was obtained from the children's parents or guardians during the study period 1982-1986 as it was required at that time when an ethics committee was not available at Universidade Federal de Pelotas.More recently, the study was approved by the Research Ethics Committee, affi liated to the National Research Ethics Council (CONEP), and written informed consent was obtained from all subjects.

RESULTS
A total of 4,296 cohort subjects provided information on physical activity.Table 1 shows the pattern of leisure-time physical activity in men and women.Walking was the least preferred physical activity among men (74% did not engage in it) and around 87% of women did not engage in any physical activity, either moderate or vigorous.The weekly score of physical activity was higher among men (334 min/wk) compared to women (112 min/wk).The proportion of men and women with a weekly score equal to zero was 28.7% and 64.5%, respectively.
Mean score of leisure-time physical activity among men was higher at the extremes of income at birth while a direct relationship was seen in women.This association was statistically signifi cant (Figure ).
Table 2 displays the prevalence of leisure-time sedentary lifestyle according to independent variables and stratifi ed by gender.The prevalence was higher in women compared to men (80.6% versus 49.2%).Family income at birth was inversely associated to sedentary lifestyle in both men and women.Those who have always been poor or have become poor during adult life were more sedentary.Men with white skin color were  more sedentary than those with black or mixed skin color.Birth weight was inversely associated to leisuretime sedentary lifestyle only among women.
Among men, the results of the adjusted analysis showed that skin color was associated to leisure-time sedentary lifestyle: subjects with Black or Mixed skin color were signifi cantly less sedentary than white ones (PR 0.84; 95% CI 0.75;0.94).Income at birth had an inverse relationship with leisure-time sedentary lifestyle.Subjects' current socioeconomic condition was associated with the outcome: sedentary lifestyle was more prevalent among those who have always been poor or have become poor during adult life (Table 3).
Similarly, income at birth was inversely associated to leisure-time sedentary lifestyle among women (Table 4).Current income was a determinant of sedentary lifestyle.Women who have always been poor or have become poor were more sedentary.Birth weight showed an inverse relationship with leisure-time sedentary lifestyle in women, even after adjusting for potential confounders.

DISCUSSION
Longitudinal studies allow to identifying determinants of diseases and risk behaviors.Better understanding factors associated to sedentary lifestyle is crucial today given the benefi ts of physical activity. 5e application of IPAQ allows the comparison of different studies because this questionnaire can provide standardized information about physical activity worldwide, validated in healthy adults. 9Although results may be inconsistent in the short and the long versions, 12 the advantage of the IPAQ -long version is that it allows the assessment of each individual domain of physical activity.
The present study found that leisure-time sedentary lifestyle is highly prevalent among young adults.This fi nding corroborates other studies that reported high prevalences of sedentary lifestyle in other age groups and more pronounced among women. 1,7,20Monteiro et al 18 reported that social and cultural factors are strong determinants of differences in sedentary lifestyle between men and women.They claim that most men associate physical activity to pleasure while women engage in these activities due to health concerns, medical recommendations and esthetics results. 1,18Besides, men tend to be more involved in group activities such as sports while women prefer individual activities such as walking and biking. 18e present study also found that men with white skin color had higher risk of sedentary lifestyle.This fi nding contrasts with that of studies in developed countries which reported higher prevalences among non-white people. 17,22On the other hand, a study conducted in Pelotas in adults (≥20 years) did not fi nd any differences in sedentary lifestyle by skin color. 7There has been no study investigating the difference of sedentary lifestyle prevalence according to skin color and stratifi ed by age.
An assumption to be tested would be that white people are more sedentary at the beginning of adult life.
Of women studied, 20% were considered non-sedentary during leisure time, and 64.5% had a score of physical activity equal to zero.The pattern of physical activity in the young adults studied is concerning given the benefi ts of physical activity. 5veral studies have investigated the effect of perinatal variables on health and disease development during lifetime. 3,15,19But the association between these variables and sedentary lifestyle, which may be a predisposing factor for disease development, needs to be further explored.
In the present study, birth weight showed an inversely proportional association with the prevalence of sedentary behavior among women.Even after adjusting for gestational age, the magnitude of the association remained unchanged.Hallal et al 13 did not fi nd an association in those born in 1993 assessed at the age of 10-12.On the other hand, Rogers et al 21 reported a potential effect of prematurity (weight ≤800 g) on motor development and of sedentary lifestyle on physical fi tness at the age of 17. 21 Victora et al 25 reported a direct relationship between birth weight and lean mass in 18-year-old men.Reduced muscle development in low-birth-weight children may explain low levels of physical activity during adolescence.

REFERENCES
In regard to leisure-time physical activity, the association between sedentary lifestyle and socioeconomic factors is the most evident.While studies assessing overall sedentary behavior (including physical activities during leisure time, at work, while commuting, and doing housework) have showed a positive association with socioeconomic conditions. 11Other studies on leisure-time physical activity showed that people with lower socioeconomic condition tend to be more sedentary. 7,10,20This can be explained by the fact that they do not have the fi nancial resources required in many leisure activities, e.g., joining a gym.In addition, knowledge on the health benefi ts of physical activity is associated to higher socioeconomic condition. 8nsidering the relevance of physical activity to health, promoting a more active life is a priority in the world's health agenda. 26Some risk factors of sedentary lifestyle such as female gender and lower socioeconomic condition have been consistently identifi ed.Similarly to that seen for other health-related factors, the most disadvantaged populations are also those less physically active, widening the inequality gap in public health in Brazil.

Figure .
Figure.Mean score of physical activity (min•wk-1) during adult life by family income at birth.Pelotas, Southern Brazil, 1982 to 2004-5.

Table 1 .
Leisure-time physical activity according to type and score of physical activity and stratifi ed by gender.

Table 2 .
Estimated prevalence of leisure-time sedentary lifestyle according to independent variables.Pelotas, Southern Brazil, 1982 to 2004-5.
* 150 subjects self-referred as Asian or native ** Chi-square test for heterogeneity *** Chi-square test for linear trend **** Information was missing in 23 (0.5%) out of 4,297 subjects in 2004-5 ***** Information on leisure-time sedentary lifestyle was missing information in one subject in 2004-5

Table 3 .
Crude and adjusted analyses of the association between independent variables and leisure-time sedentary lifestyle among men.Pelotas, Southern Brazil, 1982 to 2004-5.

Table 4 .
Crude and adjusted analyses of the association between independent variables and leisure-time sedentary lifestyle among women.Pelotas, SouthernBrazil, 1982 to 2004-2005.