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

No. In this Korean follow-up, people who were very physically active and had a normal body weight still showed the higher overall cancer rates observed among smokers and heavy drinkers. The study did not assign anyone to exercise as an antidote; it compared adults who already had different combinations of smoking, drinking, activity, and body weight.

How the comparison was made

The researchers started with 8,325,492 Korean adults who attended a national health screening program in 2002 or 2003 and had no recorded cancer. Staff directly measured height and weight to calculate body mass index (BMI), while participants reported their own smoking, drinking, and exercise habits on a structured questionnaire. Smoking was grouped as never, former, or current. Drinking was converted into grams of pure alcohol per day from how often people drank and how much they usually consumed. No drinking meant 0 grams, moderate drinking meant up to 50 grams per day. Heavy drinking meant more than 50 grams per day. Exercise was grouped by sessions per week: very active (five or more), moderate (one to four), or inactive (less than one). Body weight was grouped using BMI categories designed for Asian populations; for this study, normal weight meant below 23. These labels are study groupings, not personal weight advice. The healthiest reference group was never smokers who did not drink, had a BMI below 23, and exercised five or more times per week. A statistical survival model compared how quickly cancer or death occurred in each lifestyle combination while adjusting for age and sex; for liver cancer it also adjusted for chronic viral hepatitis because that infection strongly affects liver cancer risk.

Everyone was followed from 2002 until a cancer diagnosis, death, or 31 December 2018. During about 16 years of follow-up, 517,434 people developed cancer and 209,727 died of cancer.

What the cancer numbers showed

Compared with that healthiest group, all-cancer incidence—any newly diagnosed cancer—was higher among heavy alcohol drinkers regardless of whether they smoked. Among heavy drinkers, the higher incidence was seen in both the very physically active and the active groups, and it was seen regardless of body weight. Former and current smokers also had higher all-cancer incidence even when they did not drink. Combining current smoking with heavy drinking was associated with still higher cancer rates. The highest incidence comparisons were 1.69 and 1.62, roughly 1.6 to 1.7 times the rate in the healthiest group, among people who were former or current smokers, heavy drinkers, normal weight, and either very physically active or inactive. For specific cancers, higher lung cancer rates were observed among smokers regardless of alcohol drinking, physical activity patterns, and body weight; higher esophageal and liver cancer rates were observed with alcohol consumption. For cancer deaths, current smokers had higher cancer death rates in most combinations; the highest death comparisons, about 2.3 to 2.5 times the healthiest group, were among current smokers who were also heavy drinkers. So in the measured data, being physically active and maintaining normal weight did not offset the cancer patterns tied to smoking and heavy drinking.

What this kind of study can and cannot show

This was an observational follow-up, so people were not assigned to change their habits. It can reveal patterns that travel together in large groups, but cannot prove that smoking or drinking alone caused every extra cancer. Habits were reported only once at the start, and people may have changed their smoking, drinking, activity, or weight over the following years. Self-reports can be imprecise; people tend to overestimate exercise and underreport alcohol. The study also could not account for every other cancer risk factor, such as diet or some infections. What it shows is that in this population, having normal weight and being physically active at the start did not erase the higher overall cancer rates seen among smokers and heavy drinkers. This does not mean exercise has no benefit for an individual; it means this comparison did not erase those smoking and drinking patterns.