Exercise and a normal weight did not cancel the cancer patterns tied to smoking and heavy drinking in this large Korean follow-up.

What this study actually compared

The study began with 8,325,492 Korean adults who attended national health screening in 2002 or 2003 and had no cancer. They reported their smoking, drinking, and exercise habits, and staff measured height and weight to calculate BMI. Then the researchers followed them until cancer, death, or December 2018. Rather than assigning people to change their habits, they compared people who already lived with different combinations. The reference group was never smokers who did not drink, had a BMI below 23, and exercised five or more times a week. Heavy drinking was defined as more than 50 grams of pure alcohol per day.

What the cancer patterns showed

Compared with the healthiest group, all-cancer incidence was higher among heavy alcohol drinkers regardless of whether they smoked. Crucially, among heavy drinkers the increased risks appeared in both physically very active and active groups, and this held regardless of body weight. Former and current smokers also had higher all-cancer risk even when they did not drink. The highest rates were seen in people who were former or current smokers, heavy drinkers, normal weight, and very active or inactive: their risk of any cancer was roughly 1.6 to 1.7 times the healthiest group's. In this cohort, being physically active and maintaining normal weight did not offset the associations with smoking and heavy drinking.

Boundaries of the comparison

Because habits were reported once at the start, people may have changed their smoking, drinking, or exercise over the following years. Alcohol and activity were self-reported, so some heavy drinking may be underreported and some exercise overreported. The study cannot show that exercise has no benefit for an individual, or that every type of cancer increased. What it shows is that, in this existing-habits follow-up, people who were active and normal weight but smoked or drank heavily still had higher overall cancer incidence than the healthiest comparison group.