Study of Chinese here shows higher ideal weight for elderly and smokers
IF YOU want to fend off cancer and cardiovascular disease, keep your weight down. But people over the age of 65, as well as smokers, can afford to carry a few extra kilogrammes. That, at least, is the conclusion one can draw from a recent study of about 51,000 Chinese in Singapore, on how a person’s weight affects his risk of dying from disease.
Researchers from the National University of Singapore (NUS) and the University of Minnesota in the United States collected body mass index (BMI) data from Chinese aged between 45 and 74 years old from 1993 to 1998. They were then tracked until 2008. The researchers found that non-smokers below age 65 with a BMI of 18.5 to 21.4 had the lowest risk of dying from cancer and cardiovascular disease.
For those over age 65, the ideal BMI range was 21.5 to 24.4. This is actually higher than what the Health Promotion Board (HPB) considers “healthy” BMI. BMI is derived by dividing a person’s weight in kg by the square of his height in metres. For example, a 1.6m-tall woman weighing 52kg would have a BMI of 20.3. Under HPB guidelines, the healthy range for BMI is between 18.5 and 22.9. Those below 18.5 are considered underweight, while those between 23 and 27.4 are overweight. Obesity means having a BMI of 27.5 and above. The findings were published last month in online journal PloS One, and were part of the Singapore Chinese Health Study started by NUS and funded by the National Institutes of Health in the United States.
The study analysed data of more than 63,000 Chinese men and women for ailments such as cancer. Of the 63,000, only 51,251 were surveyed for BMI because the others were either already suffering from cancer and cardiovascular disease, or were unsure of their height and weight. Overall, the study found that it did not pay to be either too thin or too fat. Those who were underweight and obese were more likely to die ? with 25 per cent increased risk for both groups. This applied to smokers and non-smokers from all age groups. Smokers were analysed as the researchers suspected that smoking influenced the effect of BMI on death.
The study also showed that rotund smokers lived longer than their thinner counterparts. Overweight ex-smokers with BMI of 23 to 24.4, along with nearly obese current smokers with BMI 26 to 27.4, were found to be less likely to die compared to other smokers. One of the researchers, Associate Professor Koh Woon Puay, said this did not mean that smokers could eat more to override the ill effects of the habit. “Smoking affects metabolic rate differently ? it actually lowers one’s BMI,” said Prof Koh, who is from the Department of Epidemiology and Public Health at NUS. “That is why, paradoxically, the ideal BMI range for smokers is higher.” She added: “It is a bad idea to smoke to lose weight or keep yourself thin. The harmful effect of smoking exceeds that of obesity.”
The ideal BMI for those over age 65 was also found to be in the overweight range. Associate Professor Jimmy So, director of the National University Hospital’s Centre for Obesity Management & Surgery, who was not involved in the study, said it is all right for a person to be slightly overweight if he is above 65 years old. One of the reasons is that the composition of body fat changes as one ages, and not all body fat is bad, he said. “The most harmful type of fat is tummy fat,” he said. “BMI is not the perfect marker of obesity as one ages ? waistline may be a more important measure.” However, he said, the elderly should not go overboard with excessive eating, and should keep their BMI under 24.4. Prof Koh added: “More studies are needed to ascertain whether it is true that with age, one can afford to put on a few more kilos.”
A HPB spokesman said the study echoes its stance on BMI guidelines. International standards define overweight as having a BMI of 25 or more. But in 2005, HPB lowered this limit to 22.9. This is because studies showed that Asians, including Singaporeans, have a higher body fat percentage than Caucasians of the same age, gender and BMI.