Cohort study of effect of being overweight and change in weight on risk of coronary heart disease in old age

Introduction

Being overweight is an important contributor to risk of morbidity in younger people, particularly coronary heart disease.1 2 In people around age 65 heavier weight is associated with a modest increase in the risk of coronary heart disease,3 4 but it is unclear whether it is a health hazard for even older people.5 Clarification of risk associated with being overweight in late life is important as incidence of coronary artery disease increases with age, although it has been proposed that being overweight and weight gain with age carries little risk.5 In studies of weight change in old age, weight loss rather than weight gain was associated with coronary heart disease4 6 6 7 8 and weight change seemed to obscure the risk associated with being overweight.4 9

We examined the effects of being overweight and weight change on coronary heart disease in older men and women. Weights obtained roughly 10 years apart were used to estimate the risk of coronary heart disease associated with past and current weight, to determine the prevalence of weight change, to estimate the risk of coronary heart disease associated with weight change, and to evaluate whether weight change modified the estimation of risk associated with weight.

Subjects and methods

The epidemiological follow up study of the national health and nutrition examination survey I (NHANES I) is a longitudinal study of 14 407 people aged 25-74 in 1971-75.10 11 Follow up to 1987 included an in person interview in 1982-84 with measurement of weight, pulse, and blood pressure; a telephone interview in 1986 of people aged 55 or older at the time of participation in the original survey; and a telephone interview of all cohort members in 1987. Loss to follow up was less than 1% for those eligible.

For this paper we identified a cohort within the longitudinal study and followed them from 1982 to 1984. This design allowed us to use mainly measured weights to estimate change and more stringent criteria for excluding people with existing coronary heart disease. Mean length of follow up for outcome events was 3.9 (SD 0.8) years.

Our study population was aged 70 to 86 in 1982-84. We studied only white people since there were too few black participants to evaluate an interaction between race and weight. All subjects who had died before 1982-84 (n=940) or could not be located (n=3) were excluded. We also excluded 1166 people with coronary heart disease in 1982-84. This was defined as a report of heart failure, heart attack, or treatment for heart disease on interview in 1971-75; reporting at 1982-84 interview that a doctor had diagnosed a heart attack or angina; or discharge from hospital with a diagnosis of ICD-9 codes 410-414.

We excluded people with no data on weight or height in the original study and those with no weight recorded during 1982-84 (n=18). We did include reported weight for the 7% (110) who did not have weight measured in 1982-84. Mean body mass index was similar for those with estimated weight or with measured weight; reported weight has been shown to be highly correlated with measured weight.12 13 The final study population consisted of 1581 people: 621 men and 960 women.

New coronary heart disease (ICD-9 codes 410-414) in the cohort up to 1987 was determined from documentation of events in hospital discharge records (218, 83%) or from underlying cause of death on death certificates (45, 17%). There were 263 incident cases of coronary heart disease: 141 in women and 122 in men.

Procedures for measuring height and weight have been described.14 15 The 1982-84 measurements were considered as current and the 1971-75 measurements as past. We used the height measured in 1971-75 to calculate body mass index (kg/m²) for each point in time. These measures were pooled and sex specific cut off points based on thirds were calculated to be applied to both current and past body mass index, with those in the lowest third used as the reference group.16 An assessment of the effect of survival on these analyses showed that people excluded because of death were heavier in 1971-75 than those included in the cohort. Thus, our analysis is conservative since high risk heavier people have been excluded.

Weight change was calculated as percentage change from 1971-75 to 1982-84. This allows comparison of equivalent change among people of varying initial weight. We created three categories of weight change: gain of 10% or more, gain of less than 10% to loss of less than 10%, and loss of 10% or more. Those whose weight was relatively stable (gain or loss of less than 10%) were used as the reference group.

We tested the interaction between current body mass index and weight change and past body mass index and weight change. To examine how weight change affected risk of coronary disease associated with current weight, categories of weight change were crossed with categories of current body mass index to create nine analytical strata. We estimated risk of coronary heart disease in these nine strata using the thinnest weight stable group as the reference.

The risk factors for coronary heart disease included as covariates were systolic blood pressure, total cholesterol concentration (measured in 1971-75), and report of diabetes in 1982-84. Correlates of weight change included self rated health (excellent, very good, or good versus fair or poor health); alcohol intake (no intake versus any current alcohol intake); educational attainment (<9 years of education versus≥9 years); three variables estimating level of physical capacity (any difficulty versus no difficulty walking 400 m, level of usual or recreational physical activity (high, moderate, or low), or report of tiredness on usual activities); and report of serious illnesses including history of diabetes, stroke, or cancer.

Results

The 621 men and 960 women included had a mean age of 77 (SD 4) years in 1982-84. Cut off points for body mass index were 23.47 and 27.28 for women and 23.97 and 26.96 for men. More women (217, 23%) than men (76, 12%) lost 10% or more of body weight between the first and second measures while about equal proportions gained 10% or more (69 women (7%), 48 men (8%)).

Heavier body mass index in 1971-75 was associated with a 70% increase in the risk of coronary heart disease for both men and women (table 1). Heavier current body mass index was not associated with an increased risk of coronary heart disease in either men or women. Weight loss was associated with an increased risk of coronary heart disease for women (1.7 (95% confidence interval 1.2 to 2.4)) and for men (1.9 (1.2 to 3.1)). Weight gain was not associated with increased risk. Elimination of those who lost 10% or more of body weight increased the relative risk estimate among the heaviest third of current weight from 1.1 to 1.4 (1.0 to 1.9).

For men and women combined the risk associated with current weight was modified by history of weight change (multiplicative interaction term P=0.03). Risk of coronary heart disease was increased among heavier people who had gained weight and among thinner people who had lost weight (table 2).

We examined level of weight change by selected health characteristics in 1982-84 (table 3). Compared with weight stability, weight loss≥10% was related to history of diabetes and stroke, fair or poor health, and more complaints of tiredness. Those losing weight were also less physically active and reported more difficulty walking 400 metres. Those gaining weight had less education, were more likely to be former smokers, and reported more tiredness and difficulty walking distances. Controlling for these factors did not change the relation of weight and weight change with coronary risk.

Discussion

Is heavier weight a risk factor for coronary heart disease in older people? We found a risk associated with being overweight, which suggests that coronary heart disease should be added to the several health risks already associated with heavier weight in very old age.21 22 We also found that knowledge of current weight may not be sufficient to identify those at risk in old age. Weight change from middle age to old age is also an indicator of risk, particularly for thinner people who had lost weight or heavier people who had gained weight. For survivors to old age, the relative importance of weight in middle age or weight in old age is unclear. However, several studies have shown weight in middle age (which may reflect maximum weight for most people) to be most important in determining risk of coronary heart disease. Without a long term weight history clinical assessment may underestimate the risk of disease in old age.4 9

We found that weight gain, while not associated with risk overall, was associated with increased risk of coronary heart disease in heavier people. An association of weight gain with increased risk of coronary heart disease is consistent with theoretical models of the effects of weight on risk factors for coronary heart disease risk23 and recent findings in younger women.24 Why weight loss is associated with an increased risk of coronary heart disease is unclear, since weight loss should decrease the level of cardiovascular risk factors.25 26 Although direct information on reasons for weight loss were not included in our data, sustained weight loss in old age is unlikely to be voluntary27 and may reflect other diseases, some of which might increase the risk of thromboembolic events. For instance, people with diabetes and stroke were disproportionately represented in the group that lost weight. Those with weight loss were also less likely to be physically active. Although controlling for these measures did not change the results, further investigation with more frequent weight measurements, reasons for weight loss, and physiological indicators of health would be useful.