A rich new data source: Canadian population-based longitudinal data

Population-based longitudinal data are a goldmine for health researchers examining the health of a population. These data have two main advantages over previous datasets. Cross-sectional data provide a snapshot of a population at different times, but longitudinal data allow comparison of the same people over time. In addition, most longitudinal studies follow a group of people over time, but the National Population Health Survey is representative of the general household population of Canada.

Statistics Canada analysts are now demonstrating the richness of these data by examining patterns over time of health and the factors that contribute to it. We provide a sample of three recent articles published by HAMG analysts and their colleagues based on five waves of longitudinal data, 1994/95 to 2002/03.

Obesity: A growing issue
Healthy aging
Dynamics of immigrants' health
Other recent releases

Obesity: A growing issue

This study found that almost one-quarter of Canadians who had been overweight in 1994/95 had become obese by 2002/03. On the other hand, only half as many, about 10%, who had been overweight were in the normal weight range eight years later.

Nearly one-quarter of adults who had been overweight in 1994/95 had become obese by 2002/03

The study followed National Population Health Survey (NPHS) participants aged 20 to 56 at the outset of the survey. These participants were 28 to 64 in the final year of the survey.

The weight gain was not limited to overweight Canadians. The study documented that between 1994/95 and 2002/03, one-third of people who started out in the normal weight range became overweight.

Some of the findings over the eight year period:

• 38% of the men whose weight was normal in 1994/95 had become overweight compared to 28% of the women.
• 28% of the women who had been overweight became obese, compared to 20% of the men.
• Overweight men in their twenties and thirties were more likely than those in their fifties to become obese.
• Overweight men who smoked daily in 1994/95 were almost 50% more likely to have become obese than were those who had never smoked.
• Members of highest income households were 40% less likely than those in the lowest income households to become obese.
• Overweight people who were restricted in their daily activities were at increased risk of becoming obese.
• Moderate physical activity, including walking and standing, did offer overweight women some protection against obesity.

Le Petit C, Berthelot J-M. Obesity: a Growing Issue. Catalogue no. 82-618-MWE2005003.

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Healthy aging

This study suggests that unhealthy habits may not have an immediate impact on middle-aged adults but they tend to catch up to seniors as life goes on. Unhealthy behaviours such as smoking, physical inactivity and unhealthy weight were associated with decreasing chances of healthy aging among seniors (65 and older).

Among middle-aged adults aged 45 to 64, socio-economic characteristics such as the education level and household income were more important determinants of healthy aging than healthy behaviours.

Although they are harmful at any age, the consequences of unhealthy behaviours on the chances of healthy aging of middle-aged adults are not yet fully observable. The study also suggests that the benefits of healthy behaviours are cumulative through time and benefit people in the long term.

The study followed individuals who were healthy in 1994/95 during five waves of the National Population Health Survey (NPHS). Health was defined using four criteria, two related to physical health, disability and dependence, one related to mental health, and another related to self-perceived health. All criteria had to be met in order for a person to be considered in good heath.

Of course as people age, their likelihood of remaining healthy decreases. About one out of five (20%) middle-aged adults lost their good health or died between each survey cycle. Among seniors, this proportion was higher, at about one out of three (30%).

After the eight years of observation, a little more than two middle-aged adults out of five (44%) were still alive and in good health. However, this was the case for only 22% of seniors.

Among both the middle-aged and seniors, better educated individuals were more likely to remain healthy between 1994/95 and 2002/03. Among seniors, the chances of healthy aging were significantly enhanced by having a positive attitude towards life, but decreased by having chronic conditions such as arthritis, diabetes and heart disease.

Martel L, Belanger A, Berthelot J-M, Carrière Y. Healthy Aging. Catalogue no. 82-618-MWE2005004.

Dynamics of immigrants' health

When immigrants arrive in Canada, they are generally in better health than the Canadian-born population. A recent study found that 97% of new immigrants rated their health as good, very good or excellent six months after their arrival, compared with 88% for the general population. However, as time passes, this so-called "healthy immigrant effect" tends to diminish as their health status converges with that of the general population.

This new study followed initially healthy individuals across five waves of longitudinal data from the National Population Health Survey (NPHS). It showed that between 1994/95 and 2002/03, immigrants in general were more likely than the Canadian-born population to experience a shift towards fair or poor health. Moreover, recent immigrants from non-European countries who arrived in Canada between 1984 and 1994 were twice as likely as Canadian-born to report deterioration in their health during the study period.

This might suggest that these recent immigrants from non-European countries, who were initially healthy in 1994/95, adopt some unhealthy lifestyles in the process of adapting to a new culture. The study found that these immigrants were almost twice as likely as Canadian-born to have a 10% or more increase in their body mass index. As for daily smoking, no corresponding evidence was found as non-European immigrants overall were less likely than the Canadian-born to become daily smokers.

The fact that recent non-European immigrants were at higher risk of experiencing deterioration in their health is mirrored in their greater likelihood of becoming frequent visitors to the doctor (at least six consultations a year).

Ng E, Wilkins R, Gendron F, Berthelot J-M. Dynamics of immigrants' health in Canada: evidence from the National Population Health Survey. Catalogue no. 82-618-MWE2005002.

These articles are part of an Internet publication Healthy Today, Healthy Tomorrow? Findings from the National Population Health Survey, available at http://www.statcan.ca/bsolc/english/bsolc?catno=82-618-MWE. A fourth article in the series is “A step forward, a step back: smoking cessation and relapse” by Margot Shields.

Other recent releases

Joseph KS, Wilkins R, Dodds L, Allen VM, Ohlsson A, Marcoux S et al. Customized birth weight for gestational age standards: Perinatal mortality patterns are consistent with separate standards for males and females but not for blacks and whites. BMC Pregnancy Childbirth 2005; 5(1):3. http://www.biomedcentral.com/1471-2393/5/3

Ross NA, Dorling D, Dunn JR, Henriksson G, Glover J, Lynch J et al. Metropolitan income inequality and working-age mortality: a cross-sectional analysis using comparable data from five countries. J Urban Health 2005; 82(1):101-110. Summary available at /daily-quotidien/050429/dq050429b-eng.htm

Borugian M, Spinelli J, Mezei G, Wilkins R, Abanto Z, McBride ML. Childhood leukemia and socioeconomic status in Canada. Epidemiology 2005; 16(4):526-531. Summary available at /daily-quotidien/050705/dq050705b-eng.htm

Flanagan W, Boswell-Purdy J, Le Petit C, Berthelot J-M. Estimating summary measures of health: a structured workbook approach. Population Health Metrics 2005; 3(1):5. http://www.pophealthmetrics.com/content/3/1/5