“Fitness, not fat, determines life expectancy”, reads the headline of The Daily Telegraph . People “who are physically fit despite being obese suffer half the death rate of lean but unfit people”, the newspaper explains. Both the Telegraph and the Daily Mail report on the latest argument on the subject of Britain’s ongoing battle against obesity.
This story is based on a study of 2,603 US adults and found that higher fitness levels were associated with lower death rates in both fit normal weight and obese individuals. It does not suggest that overweight people were any healthier than similarly fit normal-weight people. A balanced diet and regular physical activity remain the best ways to promote a healthy lifestyle.
Dr Xuemei Sui and colleagues from the universities of South Carolina, Buffalo, and North Texas, carried out this research. The study was funded by National Institutes of Health and was published in the peer-reviewed Journal of the American Medical Association.
This was a cohort study designed to look at the relationship between fitness, body fat and death rate. The researchers followed up a group of 2,603 adults aged 60 years or older (80% were male), who were enrolled in the Aerobics Centre Longitudinal Study. Between 1979 and 2001, the participants in the study were recruited and they completed a baseline physical examination and were included as members of the study if they achieved 85% or greater of their age-predicted heart rate during treadmill examination, and had a body mass index (BMI) of 18.5 or greater.
The researchers collected other measurements either through physical examination of those participating in the study or by asking about their clinical history. This included the participant’s current health and past medical problems (e.g. past heart attacks or strokes); cholesterol and blood sugar levels; blood pressure; ECG readings (heart traces); smoking and lifestyle; percentage body fat (determined from a weighing system considering measurement of fat density and skin-folds) and fat free mass (weight minus fat mass). They grouped the participants into categories of body fat (based upon BMI) and fat free mass and into categories of fitness based upon their maximum exercise performance on the treadmill.
They followed the participants from the date of their baseline examination until the end of the study in December 2003, and followed up information about any deaths. The researchers then calculated the risk of death depending on factors such as body fat (adiposity), fitness level, smoking, age, and other medical conditions at baseline.
The average length of follow up for all participants combined was 12 years. During this period, there were 450 deaths in the sample of 2,603 people. Those who died tended to be older, with more cardiovascular risk factors, and with lower levels of fitness. There was a trend – which may have arisen by chance – towards increasing death rate with increasing BMI category, adjusted for age, sex and year of baseline examination. There was however a significant increase in death rate with high waist measurement (an indication of high abdominal obesity), when compared with normal waist circumference. There was no difference for those with a normal proportion of fat in their bodies compared to those with high fat levels. Higher death rates were also associated with abnormal ECGs at baseline and chronic medical conditions.
When they looked at fitness, the researchers found that there was a significant trend towards decreasing death rate as fitness improved. They also found that this trend for fitness was seen even after adjustment for other factors of BMI, waist circumference, body fat, general health, or smoking. The significance of waist measurement on death rate was not maintained when adjusted for fitness; however, the significance for BMI was. Those in the highest fitness groups tended to have fewer cardiovascular risk factors such as diabetes, high blood pressure, or high cholesterol.
The researchers conclude that fitness and BMI are both predictors of all-cause mortality in elderly people aged over 60. Although other measures of body fat, such as waist measurement (abdominal obesity), were significant predictors of death rate, these effects were not maintained after adjusting for fitness. They say that their findings provide more evidence of the complex relationship between body size, fitness, and long-term survival, and conclude that “enhancing functional capacity should allow older adults to achieve a healthy lifestyle and to enjoy longer life in better health”.
Age, body weight and fat, general health and fitness, and mortality are intricately related, and it is difficult to pick out one factor that has more bearing on health risk than another. This is a large and carefully conducted study in which the authors have attempted to unravel the relationships of several related factors on mortality.
, but another study in JAMA showed that although obesity had a smaller effect on mortality than was thought, it had a major impact on the prevalence of disability; the headline of the editorial asked “Is Disability Obesity's Price of Longevity?” Our aim is to add life to years not only years to life.