The study involved over 230,000 Swedish males, who were conscripted into the military aged 16 to 20 years old. Those who were in the upper ranges of overweight and those who were obese at that time were about twice as likely to develop bowel cancer over the next 35 years as those who were a normal weight.
This study has a number of strengths, including its size, the fact that body mass index (BMI) was objectively measured by a nurse and that the national cancer registry in Sweden captures virtually all cancer diagnoses. However, it was not able to take into account the boys’ diets or smoking habits – both of which affect bowel cancer risk.
Obesity in adulthood is already known to be a risk factor for bowel cancer, therefore the possibility that a person being obese from an early age also increases risk seems plausible. Maintaining a healthy weight at all ages will have a range of health benefits, such as reducing your risk of developing conditions including heart disease and type 2 diabetes, as well as a number of cancers.
Source: NHS Choices