Boston | People who have been lean all their lives are likely to live longer, while those with a heavy body shape from childhood up to middle age have the highest mortality risk, a new study has found.
Researchers from the Harvard University and Tufts University in the US tracked the evolution of body shape and associated mortality among two large cohort studies. In total, 80,266 women and 36,622 men in the study recalled their body shape at ages 5, 10, 20, 30, and 40 years.
They also provided body mass index at age 50, and were followed from age 60 over a median of 1516 years for death. They answered questionnaires on lifestyle and medical information every two years, and on diet every four years.
Results showed that people who remained lean throughout life had the lowest mortality, with a 15year risk of death being 11.8 per cent in women, and 20.3 per cent in men.
Those who reported being heavy as children and who remained heavy or gained further weight, especially during middle age, had the highest mortality, with a 15year risk of death being 19.7 per cent in women and 24.1 per cent in men. In a second study, researchers confirm that increasing levels of body mass index (BMI) are associated with higher risks of premature death.
The BMI is an established way of measuring body fat from the weight and height of a person, but the optimal BMI associated with the lowest mortality risk is not known.
It is expected that a higher BMI is associated with a reduced life expectancy, but the largest previous study showed that when compared with normal weight, overweight was associated with reduced mortality, and only high levels obesity were associated with increased mortality.
However, there were various limitations in the study, for example, smoking and prevalent or prediagnostic illness were not taken into account, both of which can lead to lower body weight, and increased mortality. So researchers in the current study sought to clarify this association by carrying out a large metaanalysis of 230 prospective studies with more than 3.74 million deaths among more than 30.3 million participants.
They analysed people who never smoked to rule out the effects of smoking, and the lowest mortality was observed in the BMI range 2324 among this group. Lowest mortality was found in the BMI range 2223 among healthy never smokers, excluding people with prevalent diseases.
Among people who never smoked, and studied over a longer duration of follow up of more than 20 and 25 years, where the influence of prediagnostic weight loss would be less, the lowest mortality was observed in the BMI range 2022. The research was published in the journal BMJ.