Health consequences in adults with low birth weight studied

Published in The Hindu on March 15, 2012

A unique study has found that male adults born more than 20 years ago with low birth weight (LBW) show differences in muscle mass, fat content and diastolic blood pressure compared with those born with normal body weight.

The study was done on adults from a rural area (Kaniyambadi) near Vellore, Tamil Nadu. The results were published recently in the European Journal of Endocrinology.

In total, 117 adults born at the Christian Medical College (CMC), Vellore, Tamil Nadu between 1986 and 1990 were recruited. Of these, 61 belonged to the low birth-weight category (less than 2.45 kg), while the rest had normal birth weight (between 3.1 kg and 3.5 kg). Low birth weight refers to individuals who weighed less for a given gestational age at birth.

The study gains importance as nearly 30 per cent of infants born in India are underweight (less than 2.5 kg). The primary reason for this is the under-nutrition in women before and during pregnancy.

This study, which looked at people who are more than 20 years old, provides vital information on what the long-term health effects are when born with low birth weight. The study has a limitation — there is no information on growth parameters collected at regular intervals during the last 20 years, particularly during childhood.

Babies who are underweight preserve their body fat at the cost of muscle mass even at the foetal stage. As a result, the muscle mass in these individuals is less than those with normal birth weight.

“Those adults born with low birth weight had reduced lean body mass than those with normal birth weight,” said Dr. Nihal Thomas, Head of the Department of Endocrinology, Diabetes and Metabolism, CMC, Vellore. He is the first author of the paper. Lean body mass refers to muscle mass. Muscles play an important role in glucose uptake and hence reduced muscle mass may probably increase the possibility of these individuals developing insulin resistance at a later stage.

“There is more risk of developing diabetes at a later stage when the muscle mass is less,” Dr. Thomas said. “So reduced lean body mass is an early marker for diabetes.”

Apart from reduced lean body mass, adults with low birth weight had decreased total mineral content.

Males belonging to both groups showed normal insulin sensitivity. However, five males (nearly 10 per) who had low birth weight had impaired glucose tolerance (IGT), an early stage of diabetes. However, the study has no information on physical activity of the individuals. According to him, unpublished data shows that there was no difference in physical activity between the two groups.

Blood pressure

They also found that adults with low birth weight had higher diastolic blood pressure (2 mm Hg) than the control group. According to him, even this small difference is significant.

“Even though the difference is only 2 mm Hg, this difference is seen at an early age and in those with low Body mass index (BMI),” Dr. Thomas said. “As they grow this difference would probably become even more significant.”

Explaining the reason behind the increased blood pressure seen in the LBW group, he said, “the nephrone mass in the kidneys appear to be lower and their ability to excrete sodium [salt] is lower. Hence the retention of salt increases blood pressure.”

The adults who belonged to the low birth weight group were also relatively shorter than the control group. However, the parents of these people were also shorter than the control group. Hence a strong link between weight and height cannot be established.