Sometimes it's hard to work up the motivation to eat healthy or work out, but a new study might be a push in that direction.

Being overweight or obese is linked to 10 common cancers. Scientists estimate that extra weight could be a factor in more than 12,000 cases of cancer every year.

According to a study published in Lancet medical journal, if high levels of obesity continue, this could mean an additional 3,700 cases of cancer per year.

This study looked at five million people, the largest so far to confirm a link between obesity and cancer. The data came from the UK's Clinical Practice Research Datalink. They followed participants for an average of 7.5 years.

Researchers at the London School of Hygiene and Tropical Medicine found that each 13 to 16 kg of extra weight was ranked linearly to greater risk of six cancers.

The risk varied by cancer type, but cancer of the uterus had the highest increased risk followed by gall bladder, kidney, cervix and thyroid, while leukemia had the lowest rise in risk.

"There was a lot of variation in the effect of BMI on different cancers," said Dr. Krishnan Bhaskaran, who led the research. "For example, risk of cancer of the uterus increased substantially at higher body mass index, for other cancer, we saw a more modest increase in risk or no effect at all. This variation tells us BMI must affect cancer risk through a number of different processes, depending on cancer type."

High body mass index is related to higher risk of cancer in the liver, colon, ovaries and post-menopausal breast cancer. Though there is some evidence that shows a higher BMI may be associated with a lower risk of prostate cancer.

In the US, more than 69 percent of adults are overweight or obese. In the UK, 62 percent of individuals are considered overweight or obese.

Obesity is also related to serious health conditions such as diabetes, heart disease and stroke.

Researchers believe that an eight to 10 pound increase in average BMI would cause an additional 3,790 cases of the 10 cancers every year.

"The number of people who are overweight or obese is rapidly increasing both in the UK and worldwide," Bhaskaran said. "It is well recognized that this is likely to cause more diabetes and cardiovascular disease. Our results show that if these trends continue, we can also expect to see substantially more cancers as a result."