Obesity is a risk factor for cancer, but researchers are only now unfurling the exact mechanisms behind this connection. A new study looks at how obesity might scupper the immune system's ability to attack tumor cells.

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Obesity may reduce the immune system's ability to attack tumor cells.

Obesity is at an all-time high in the United States.

According to the National Institutes of Health, two-thirds of adults in the U.S. are either obese or overweight.

Obesity increases the risk of developing a number of health conditions, including type 2 diabetes, hypertension, cardiovascular disease, and kidney disease.

Similarly, obesity increases the risk of developing certain cancers, including endometrial cancer, liver cancer, pancreatic cancer, and colorectal cancer.

In fact, an estimated 40 percent of new cancer diagnoses are associated with obesity.

Though the relationship between obesity and cancer risk is now well-documented, we do not have a full understanding of why this relationship exists. It is probable that there are a number of ways in which they are linked.

For instance, fat cells release hormones and growth factors that tell our body's cells to divide more often; this increases the chance that cancer cells will be produced. However, this is not the full picture.

Obesity and natural killer cells

A recent study adds another piece to the obesity-cancer puzzle. Researchers from Trinity College Dublin in the United Kingdom and Harvard Medical School and Brigham and Women's Hospital, both in Boston, MA, conducted the research.

They recently published their findings in the journal Nature Immunology.

Prof. Lydia Lynch, an associate professor of immunology at Trinity College Dublin, led the research. She explains why this line of investigation is so important:

"Despite increased public awareness, the prevalence of obesity and related diseases continue. Therefore, there is increased urgency to understand the pathways whereby obesity causes cancer and leads to other diseases, and to develop new strategies to prevent their progression."

The scientists were interested in observing the effect of obesity on immune surveillance, which is a process wherein the immune system hunts out cancerous or precancerous cells and destroys them before they can cause harm.

In particular, the researchers focused their investigation on natural killer (NK) cells, a type of white blood cell known to lead the charge against tumor cells. They used immune cells taken from humans and mice in a series of insightful experiments.

Fat-clogged cells

They saw that in people with obesity, the NK cells' cellular machinery becomes clogged up with fat. Although the NK cells can still find and bind to tumor cells, they can no longer destroy them.

In other experiments, they pinned down the metabolic step that fat buildup hinders. Importantly, the scientists demonstrated that by giving these clogged NK cells a metabolic jolt, they were able to reignite their cancer-killing powers.

This provides hope that experts might one day develop treatments as a result of understanding this mechanism.

"Our results highlight immunometabolic pathways as a promising target to reverse immune defects in obesity, and suggest that metabolic reprogramming of natural killer cells may kick-start their anticancer activity and improve treatment outcomes."

Prof. Lydia Lynch

This study is among the first to look at obesity's impact on immune surveillance. It provides fresh insight, and more work is sure to follow. Because obesity is so incredibly prevalent, any glimpse into its biochemical impact is timely and important.