In , we examined the weight history and baseline characteristics of adult cohort members by category of baseline BMI. As previously reported in other analyses (8
), the baseline characteristics of this cohort indicate a low prevalence of cigarette smoking, alcohol use, and animal product consumption. The results on prebaseline weight history and baseline disease in are discussed below.
Weight history (17 years before baseline) and selected baseline characteristics of 7,855 cohort members of the Adventist health study I are given by category of baseline BMI
Prevalence of a history of overweight or obesity (17 years prior to baseline)
In , we found that the prevalence of a history of overweight or obesity (>25 kg/m2) 17 years prior to baseline was 10.6% among the underweight (<19 kg/m2 at baseline) and 20.4% among adults in the recommended range (19–25 kg/m2 at baseline). Among cohort members who were overweight at baseline, 8.3% had been obese 17 years before baseline.
Thus the findings indicate that 10–20% of the “low baseline BMI” subjects typically used as a “referent category” (<19 kg/m2, 19–25 kg/m2) when calculating the risk of obesity were once overweight or obese themselves. This trend raises the possibility that some of this weight loss occurring before baseline was due to obesity-related disease. In this context, we note that among cohort members who were underweight at baseline there was a greater prevalence of coronary heart disease, cancer, and stroke.
Relation between history of overweight or obesity (17 years prior to baseline) and age at baseline
We further stratified the analysis of weight history by age at baseline. In , we found that in those adults who were underweight at baseline, the prevalence of a prebaseline weight loss from an overweight or obese state substantially increased with age to the point that it tripled for the oldest old (21% for >85 years) relative to the younger adults (6% for <65 years). For those adults who were in the recommended range at baseline (), a similar trend with age occurred where the prevalence of prebaseline weight from an overweight or obese state was about threefold higher in the oldest old (37.0% for ≥85 years) relative to the younger adults (12.6% for <65 years). Also, among those adults who were overweight at baseline () the prevalence prebaseline weight loss from a BMI >30 kg/m2 was threefold higher for the oldest old relative to the younger adults.
Prevalence of history of overweight/obesity (>25 kg/m2 at 17 years before baseline) among adult cohort members who were underweight (<19 kg/m2) or in the recommended range of BMI (19–25 kg/m2) at baseline
Prevalence of history of obesity (>30 kg/m2) among 2,510 adult cohort members who were overweight (>25–30 kg/m2) at baseline
Thus, the findings indicate that in the oldest old, 20–37% of the “low baseline BMI” subjects typically used as a “referent category” (<19 kg/m2, 19–25 kg/m2) when calculating the risk of obesity or overweight were once overweight or obese themselves. Again, the possibility that weight loss from obesity-related disease is adding an increasing number of lean elderly with co-morbidities to analyses of baseline BMI and mortality needs further examination in the data.
Relation between history of weight loss (≥25 kg/m2 to lower BMI, ≥30 kg/m2 to lower BMI) and disease at baseline
In , we conducted a multivariable logistic regression analyses (adjusted for age, sex, ever-smoking) to determine which diseases were associated with weight loss from >25 kg/m2 at 17 years before baseline to 19–25 kg/m2 at baseline (loss of 5 kg/m2 by difference in category medians). We found that adults who lost weight from >25 kg/m2 to 19–25 kg/m2, were more likely to have been diagnosed with diabetes (odds ratio (OR) = 2.91 95% confidence interval (CI) (2.16, 3.93)), coronary heart disease (OR = 1.84 95% CI (1.42, 2.40)), high blood pressure (OR = 1.51 95% CI (1.26, 1.82)), or asthma (OR = 1.32 95% CI (0.94, 1.87)). In , we also found that those who lost weight from >30 kg/m2 to 19–25 kg/m2 were about two times (OR = 1.97 95% CI (0.88, 4.38)) more likely to have been diagnosed with cancer. When considering whether the weight loss (from overweight/obesity) in the adults in the recommended range in is due to disease pathology it is also noteworthy that the prevalence of disease in this group tended to increase from age <65 years (coronary heart disease, 6.1%; cancer, 3.9%; stroke, 0%; high blood pressure, 23.1%; diabetes, 8.5%; asthma, 7.6%) to age >65 years (coronary heart disease, 18.9%; cancer, 10.5%; stroke, 6.8%; high blood pressure, 36.6%; diabetes, 14%) for all outcomes but asthma.
Prevalence and odds ratio of disease associated with weight loss from a BMI of >25 kg/m2 measured 17 years before baseline to a BMI of 19–25 kg/m2 measured at baseline (loss of 5 kg/m2 by difference in category medians)
We also conducted multivariable analyses (adjusted for age, sex, ever-smoking; not shown in the tables) to determine which diseases were associated with an even larger weight loss from >25 kg/m2 at 17 years before baseline to <19 kg/m2 at baseline (a loss of 9 kg/m2 by difference in category medians). Weight loss at this level was associated with greater odds of stroke (OR = 11.55 95% CI (3.06, 43.66)), high blood pressure (OR = 5.20 95% CI (2.42, 11.20)), diabetes (OR = 4.41 95% CI (1.45, 13.47)), and coronary heart disease (OR = 1.86 95% CI (0.78, 4.42)).
We also considered in multivariable analyses (adjusted for age, sex, ever-smoking; not shown in tables) which diseases were associated with loss of weight from obesity (>30 kg/m2) at 17 years before baseline to overweight at baseline (>25–30 kg/m2) and found that this type of weight loss was associated with diabetes (OR = 2.60 95% CI (1.70, 3.97)), high blood pressure (OR = 2.07 95% CI (1.51, 2.83)), and stroke (OR = 1.96 95% CI (0.97, 3.96)).
Excluding subjects with prebaseline weight loss from a survival analysis of baseline BMI and mortality
We conducted a survival analysis that related baseline BMI to 12-year risk of mortality among AHS I Cohort members (). To examine confounding by obesity-related disease, we present in an analysis that excludes those adults in of BMI 19–25 kg/m2 at baseline who had experienced a prebaseline weight loss of 5 kg/m2 from an overweight or obese (>25 kg/m2) state at 17 years before baseline. To examine confounding by weight loss in all subjects we also present analysis in that excludes all subjects with prebaseline weight loss of 5 kg/m2 or more during the 17 years before baseline.
Table 5 Age-adjusted hazard ratios (hr) relating overweight (>25–30 kg/m2) and obesity (>30 kg/m2) to all-cause mortality are computed relative to the recommended range of weight (19–25 kg/m2) in analyses of 7,855 ahs cohort members (more ...)
Among all men and women in , the age-adjusted findings indicate significant 57–58% increases in risk for obesity relative to 19–25 kg/m2; no association was found with overweight in these models. Exclusion of adults who experienced prebaseline weight loss from an obese or overweight state (>25 kg/m2 prebaseline to 19–25 kg/m2) strengthened the findings for obesity to significant 70–80% increases in risk (relative to 19–25 kg/m2) and also revealed a significant 27% increase in risk for overweight (relative to 19–25 kg/m2). In age-stratified analyses, this effect was more evident in the elderly (≥65 years) than the nonelderly (<65 years). Exclusion of adults indicating any prebaseline weight loss of 5 kg/m2 or more also strengthened the risk estimates for baseline overweight and obesity, but not to the same extent as the exclusion weight loss following a history of excess adiposity. Multivariable adjustment for other variables (smoking, alcohol, vegetarian status, physical activity) did not alter these results.
To determine the effect aging on these results, we ran models with interaction terms for Categories of BMI (<19, 19–25, >25–30, >30 kg/m2
) × Age (<65 years, ≥65 years). The log likelihood ratio test for these terms indicated a significance for the interaction among women (P
< 0.001), but not men (P
= 0.70). We have previously reported such effects indicating a direct relation between BMI and Mortality among men (no interaction with age), and an increased risk for lean women that emerges during menopause (interaction with age among lean women (8
)). Overall, any evidence of interaction with age does not negate the findings that both overweight and obesity become strong risk factors even among older (age ≥65 years) men and women after accounting for weight loss.