A new study reveals links between BMI, diabetes, and liver cancer.
Liver cancer, as the name suggests, starts in the liver, rather than traveling there from another organ or tissue; it is relatively uncommon but serious.
The American Cancer Society estimate that there will be 39,230 new cases of liver cancer and 27,170 deaths from the disease in America in 2016.
Globally, around 700,000 people are diagnosed each year.
Because symptoms do not become apparent until the disease has progressed substantially, cases of liver cancer are often caught relatively late.
As Peter Campbell, author of the present study, says, "the prognosis for patients diagnosed with this type of cancer is especially grim."
The exact causes of liver cancer are not known, but most cases are associated with damage and scarring of the liver, referred to as cirrhosis. Known causes include alcohol abuse and hepatitis B and C infection.
Although liver cancer is fairly rare in America, since 1980, the incidence has more than tripled.
Why has liver cancer incidence increased?
It is well known that type 2 diabetes is on the rise in the United States, and this surge runs in parallel with a boom in average waist circumference and a sharp increase in obesity. As Campbell says: "All three relate to metabolic dysfunction."
A team of researchers from the National Cancer Institute decided to investigate whether there could be links between these three obesity-related parameters and the rise in liver cancer.
Campbell and his team collated data from 1.57 million participants enrolled in 14 separate U.S.-based studies. In each study, questionnaire data was gathered at the start relating to weight, waist size, height, tobacco usage, alcohol intake, and other cancer-related risks.
Overall, type 2 diabetes occurred in 6.5 percent of study participants and 2,162 developed liver cancer.
Once the data had been analyzed, the team found that for every increase in body mass index (BMI) of 5 kilograms per meter squared, there was a parallel increase in liver cancer risk; this equated to a 38 percent increase in men and 25 percent in women.
As for waist circumference, every 5-centimeter extension increased the risk by 8 percent.
Once the findings had been adjusted for smoking, race, alcohol intake, and BMI, individuals with type 2 diabetes were 2.61 times more likely to develop liver cancer; this risk increased in line with BMI.
"The lifetime risk for liver cancer in the United States is about 1 percent; approximately eight adults per 100,000 will develop liver cancer in a given year. For adults with type 2 diabetes mellitus, their risk of developing liver cancer is more than doubled relative to those who do not have type 2 diabetes mellitus, according to this study."
Peter Campbell, Ph.D.
New risk factors for liver cancer
The results show that the three factors - BMI, waist circumference, and type 2 diabetes - all increased the risk of developing liver cancer.
The list of obesity-related cancers already includes colorectal cancer, postmenopausal breast cancer, and cancers of the kidney, endometrium, thyroid, and gallbladder. As Campbell says, these results now give "substantial support to liver cancer being on the list of obesity-associated cancers."
Although this study does not prove that the rise of liver cancer is purely down to obesity, it demonstrates that it is more than likely involved. Liver cancer will no longer be considered the sole domain of alcohol abuse and hepatitis.
Senior investigator Katherine A. McGlynn drives home the importance of the study:
"From a public health perspective, these results are very important because obesity and diabetes, unfortunately, are common conditions in the population. While some other well-described risk factors, such as hepatitis B virus or hepatitis C virus, are associated with increased risks of liver cancer, these factors are much less common than are obesity and diabetes."