Can Exercise Protect Against Liver Cancer? Possibly, Suggest Two New Studies
There is plenty of strong evidence that exercise reduces the risk of several types of cancer and plays a key role in cancer prevention. Yet for liver cancer, specifically, the research is not as clear.
Now, two recent studies add to the body of research that indicates exercise may offer some protection against liver cancer – a cancer for which incidence rates are increasing in the US and have already more than tripled since 1980. One is a laboratory study focusing on the role of obesity and diabetes; the other tracked a large group of people and looked at their activity levels. Both offer important insights into the role of exercise in potentially reducing the risk of liver cancer, and the need for further study.
AICR’s latest report – an analysis of the worldwide research – found the research to be generally consistent and suggestive that being more physically active lowers the risk of liver cancer. But the evidence was too limited to be more certain that activity actually caused the risk reduction.
An increasing proportion of liver cancers are linked to Non-Alcoholic Fatty Liver Disease (NAFLD). As its name suggests, NAFLD is not connected to heavy alcohol intake that is a strong risk factor for liver cancer. Having excess body fat and type 2 diabetes increase the risk of developing NAFLD and a severe type of NAFLD — called non-alcoholic steatohepatitis (NASH) — causes inflammation, liver cell damage and increases the risk of liver cancer.
In the lab: exercise, obesity, diabetes and liver cancer
In the laboratory study, the researchers looked at the effect of exercise on the development of liver tumors in mice with obesity and insulin resistance (similar to type 2 diabetes). This model is more similar to how the disease develops in humans, than had been attempted previously.
The study used mice that are genetically prone to obesity and insulin resistance. Half of the mice were given regular access to a running wheel; the other half remained sedentary. All of the mice were given a low dose of a substance that accelerated the development of liver tumors. For three months the exercising mice weighed less than the sedentary group, but at six months even the exercising group had developed obesity.
After three months, the exercising group showed less signs of abnormal cells in the liver compared to the sedentary group. After six months, far fewer exercising mice had developed liver tumors compared to the sedentary group.
The study then identified specific signaling pathways active in the exercising group that may have played a potential role in the cancer protection.
The findings in this laboratory study are similar to the conclusions of AICR’s report that concluded physical activity may reduce the risk of liver cancer by improving how sensitive the body is to insulin. That, in turn, can lead to healthier levels of blood sugar, regardless of weight.
In the human world: Brisk walkers and lower risk
In the second study, researchers looked at activity levels of human data and potential links to liver cancer. The study, published in Cancer Prevention Research, included data from approximately 122,000 people who were participants in the long-running Nurses’ Health Study and the Health Professionals Follow-up Study.
Participants answered questions about their activity patterns when they started the study and at regular intervals throughout the years. They also reported information about relevant lifestyle habits, weight, diabetes and other risk factors. All participants were cancer-free when the study began.
After an average of 23 years, 138 people had been diagnosed with primary liver cancer. There was no link found between total physical activity and liver cancer, but when the study teased apart activity categories, it found that brisk walking was linked to lower risk. This link held after taking into account alcohol intake, BMI, type 2 diabetes and other key risk factors.
People who spent over one hour a week walking briskly had a 44 percent lower risk of developing liver cancer compared to non-brisk walkers.
The study also showed a link between moderate-intensity activity and lower risk of liver cancer, but this link did not hold up after adjusting for BMI and type 2 diabetes. There was also no link between vigorous activity and lower risk.
Some study limitations noted in the paper include the relatively small number of cancer cases, meaning that the results may also be due to chance. Also, the activity levels may be inaccurate because they were self-reported. This study only included leisure-time activities in their vigorous category, as opposed to being active at work, so some people may have been misclassified as less active than they actually were.
Given these limitations, more research is needed to confirm these findings and understand the mechanisms.
Lowering your liver cancer risk
For now, the evidence for physical activity lowering liver cancer risk remains limited but suggestive. Yet there is strong evidence that physical activity offers cancer protection in general. AICR’s latest report found that physical activity lowers the risk of breast, colorectal and endometrial cancers. It also helps maintain a healthy weight, which plays a key role in lowering risk of at least a dozen types of cancers.
Infection with hepatitis B and C and high alcohol intakes remain important risk factors for liver cancer in Americans. Vaccines are available for some types of hepatitis and AICR research shows that staying a healthy weight and limiting alcohol to moderate consumption, if at all, can also lower the risk (approximately three or more alcoholic drinks a day is a cause of liver cancer.) There is also strong evidence that coffee can protect against this cancer.
For more on the latest research related to physical activity and cancer, sign up for AICR’s email publications.
The Journal of Hepatology study was funded by the Australian National Health and Medical Research Council, the Australian Capital Territory Cancer Council and the Veterans Affairs Biomedical and Laboratory Research and Development Grant.
This announcement was originally released on May 19, 2020, by the American Institute for Cancer Research. It is republished with permission.