SINGAPORE, May 3 (Xinhua) -- Not only those with overweight problems face higher risk of colon cancer, but the skinny folk are also in the same boat, a latest study has found, local media reported Tuesday.
The surprising finding emerged from the Singapore Chinese Health Study, a long-term research involving more than 50,000 participants and funded by the United States National Cancer Institute, local daily Straits Times reported on Tuesday.
Among those with a good body-mass index (BMI) of 21.5 to 24.4, only 89 out of 100,000 had colon cancer, the study found. Among those with BMIs of 18.5 to 21.4 and 24.5 to 27.4, the number of cases went up to 103.
And among those with BMIs of 18.5 or less, or the skinny folk, the incidence shot up to 119 or 33 percent higher than the ideal group, the study found.
The BMI is calculated by dividing the weight by the square of height, all in metric form. A person who is 1.65 meters tall and weighs 50 kilograms would fall in the skinny category, which makes up about 7.5 percent of the study group of 63,000 aged between 45 and 74.
Among those with a BMI of 27.5 or above, the incidence of colon cancer was 130 out of 100,000, about 46 percent higher than the ideal group.
The results surprised the research team, whose members included researchers from the University of Minesota in the United States.
Koh Woon Puay, a researcher at the National University of Singapore and the principal investigator of the study, said, "We are trying to understand how this is biologically plausible."
The researchers suggest in their paper that the higher risk of colon cancer among underweight people could be due to something called "oxidative DNA stress," or mild inflammations that hit the underweight, damaging their immune system and allowing cancer cells to proliferate.
This is unlike what causes cancer in the overweight, who are believed to have more insulin in their system, which might be responsible for decreasing the body's ability to prevent tumors from forming.
The researchers also covered rectal cancer, but find there was hardly a difference between the different groups.
Koh said the results of the study could apply across all races, as the studies in Japan and South Korea also found a link between obesity and a higher risk of colon cancer.
The colorectal cancer has become the top cancer in Singapore, with the Chinese more likely to get it than the Malays and Indians, according to figures from Singapore's cancer registry. Chinese men are twice as likely as Malay men and three times as likely as Indian men to get colorectal cancer.
The finding will be published in Cancer, the journal of the American Cancer Society in June.