WINSTON-SALEM, N.C. -- If patients are overweight or obese when they reach age 70, matters will probably get worse over the next decade, when aging bodies gain fat and lose lean mass in these vulnerable years, researchers reported.
WINSTON-SALEM, N.C., Feb. 7 -- If patients are overweight or obese when they reach age 70, matters will probably get worse over the next decade, when aging bodies gain fat and lose lean mass in these vulnerable years, researchers reported.
They studied patients when they were in their 70s, those born in 1918 up to those born in 1927. Interestingly, those born later-those who spent more younger years when obesity in America started to increase in the late 1970s-had a higher percentage of body fat compared with the former, the investigators found.
From 1976-1980 to 1999-2000, the rate of obesity doubled in older adults, reported Jingzhong Ding, M.D., Ph.D., of Wake Forest University here, and colleagues, in the February issue of the American Journal of Clinical Nutrition. Previous studies have not addressed how body composition has changed with the increasing prevalence of obesity, they said.
Later male cohorts had a greater percent body fat (0.32% per birth year, P<0.0001) compared with earlier cohorts. This cohort effect was due to a greater increase in fat mass than in lean mass (0.45 versus 0.17 kg per birth year). For example, among 80-year-old men, those born in 1927 had about 10 pounds more fat compared with those born in 1918.
The Health, Aging and Body Composition Study included 1,786 well-functioning, community-based whites and blacks (52% women and 35% blacks), ages 70 to 79 at the time of enrollment, a critical period for the development of disability, the researchers said. Participants came from Pittsburgh and Memphis.
The researchers divided the participants into 10 groups on the basis of their birth years (from 1918 to 1927). Body composition was measured by annual dual-energy x-ray absorptiometry over a five-year follow-up, until all patients were 84.
At baseline for men, percent body fat, fat mass, and lean mass (bone-free) were 28 5% (mean standard deviation), 24 7 kg and 56 7 kg, respectively.
At baseline for women, percent body fat, fat mass, and lean mass (bone-free) were 39 6%, 28 9 kg, and 40 6 kg, respectively.
With increasing age, the percent of body fat in men initially increased and then leveled off after age 80. This age-related change was due to an accelerated decrease in lean mass, and an initial increase and a later decrease in fat mass, the researchers said.
The pattern was similar in women, although the initial increase was less rapid.
Mixed models were used to assess the cohort effect and age-related changes on body composition.
As in men, later cohorts in women had a greater percent body fat (0.16 percent per year) than earlier cohorts. The increase in percent body fat was also due to a large increase in fat mass (0.34 kg per year) and a moderate increase in lean mass (0.18 kg per year). With increasing age, both percent body fat and fat mass increased from age 70 to 80 and then leveled off from ages 81 to 84, the researchers reported.
The study indicated that even though the amount of fat mass was less than that of lean mass, the increase in fat mass was greater that that of lean mass, Dr. Ding and colleagues said. Therefore, each successive cohort from 1918 to 1927 had a greater increase in percent body fat.
These changes in body composition may be attributed to sedentary lifestyles and increased caloric intake, the researchers said. Although the association of fat mass with mortality in older adults is controversial, excess fat mass is still associated with a greater burden of type 2 diabetes, cardiovascular disease, hypertension, and dyslipidemia.
In reviewing the study's limitations, the investigators urged caution in interpreting the results, since the findings cannot be generalized to other age groups. Second, they said, the present analysis was limited to participants who remained alive during the five-year follow-up.
Also, they said, only well-functioning elderly were recruited for the study. The older participants, who represented earlier cohorts, might be even more selective than the younger participants with regard to physical function. If better physical function is associated with lower percent body fat, the decreased percent of body fat in earlier cohorts may be partly due to selection bias. However, this should not have affected the assessment of age-related changes in body composition, the researchers said.
The underlying mechanisms of age-related changes in body composition are still unclear, the researches said, although a decline in basal metabolism and impairment in the ability to regulate energy balance may be contributing factors. Importantly, from a clinical perspective, these age-related changes in body composition may underlie many age-related diseases.
The confluence of birth cohort and age on body composition results in bigger body size and less lean mass among the elderly. "Our data may portend a growing burden of body composition-related health conditions should body composition trends continue," the researchers said.
The impact of sarcopenic obesity -- increase in fat mass and loss of skeletal muscle -- may be dramatic in the coming years. "As a result, the development of appropriate interventions that target fat loss while preserving skeletal muscle to prevent disability and other illnesses in the elderly is of great public health importance," Dr. Ding's team concluded.