Being good at cardio when you're young could lower your risk of 9 types of cancer later in life, according to a study

Researchers found that being fit between the ages of 16 and 25 was associated with lower risks of certain types of cancer, particularly ones that affect the GI tract.

• Being fit between the ages of 16 and 25 was linked to a lower risk of developing cancer in a study.
• The study looked at over one million conscripts in Sweden over a three-decade period.
• But "some physical activity is better than none," a co-author of the study said. 

Having a good level of cardio fitness when you're young could lower the risk of developing certain cancers later in life by up to 42%, according to a study.

Lead author Dr. Aron Onerup, a post doctoral researcher at the University of Gothenburg's Institute of Clinical Sciences, Sweden, told The Guardian he was surprised by the consistent links found in the study between cardiorespiratory fitness and a lower risk of cancers in the gastrointestinal tract in particular.

The study, published in the British Journal of Sports Medicine on Tuesday, used data from a register of 1,078,000 Swedish men who completed military conscription between 1968 and 2005. They were all aged between 16 and 25 at the beginning of the study, and their health was followed for an average of 33 years. 84,117 (6.9%) of the men developed cancer more than five years after conscription.

The men were split into three categories: those with low levels of cardiorespiratory fitness, those with moderate CRF, and those with high CRF. This was measured by monitoring their heart rates as they pedaled on an exercise bike with increasing resistance. The longer they could keep cycling on as high a resistance they could stand, the better their CRF.

Better cardio fitness was linked with a lower risk of developing various cancers

The researchers found that those who had higher CRF when they were younger had between a 20% and 40% lower baseline risk of developing gastrointestinal cancers.

CRF was also linked with a 42% lower risk of lung cancer, a 40% lower risk of liver cancer, and a 39% lower risk of esophagus cancer.

A 21% lower risk of stomach cancer, a 20% lower risk of kidney cancer, an 18% lower risk of bowel cancer, as well as lower risks of rectal, pancreatic, and head and neck cancers were also linked to higher CRF.

Men with a higher CRF were also 7% more likely to develop prostate cancer and 31% more at risk of skin cancer, which the researchers said could be due to increased prostate cancer screenings during the period of study, and those men being exposed to more UV rays.

Regardless, Onerup said that "more physical activity is better for optimal health outcomes," but that "some physical activity is better than none," so it's never too late to get the health benefits of getting fit.

Insider recently reported that being physically fit is one of the eight major habits for living a longer, healthier life, and that any type of exercise is beneficial.

Dr. Claire Knight, senior health information manager at Cancer Research UK who wasn't involved in the study, told The Guardian that this study "doesn't fully take into account the effect of diet, alcohol, and smoking, which are more likely to affect your risk of developing cancer."

It was also an observational study, so researchers said that this limits any conclusions they could make about the causes of cancer.

Dr. Melinda Irwin, associate dean of research at Yale Cancer Center who also wasn't involved in the study, told Medical News Today that the link could be because higher CRF leads to "improved metabolic, inflammatory, and immune function," which reduces the risk of developing cancer.