A pandemic of childhood obesity may be contributing to higher rates of cancer, as well as more aggressive cancers, in people under the age of 50.

The number of young adults receiving cancer diagnoses is growing. Many of these cancers have typically been associated with people over age 50.

Childhood obesity can take some of the blame.

A meta-analysis by Case Western Reserve University School of Medicine researcher Dr. Nathan A. Berger shows that as obesity is increasing in the younger population, so is cancer.

And those cancers tend to progress faster.

For the review, Berger compiled evidence from more than 100 publications.

He included animal studies, clinical trials, and public health data.

In this study, young adults are those under age 50.

A normal body mass index (BMI) is between about 18 and 25. A BMI of 25 to about 30 is considered overweight, and a BMI of 30 or more is obese. A BMI of 40 or more is severe or morbid obesity.

The analysis highlights how excess body fat increases the risk of 13 types of cancer.

Nine of the 20 most common cancers in the United States usually diagnosed after age 50 are now reported more frequently in younger adults.

The review found that in 2016, 1 in 4 new cases of thyroid cancer involved people between the ages of 20 and 44. For breast cancer, it was 1 in 10.

For decades, the peak incidence age of multiple myeloma has been 69. Now it’s being reported more frequently in young adults under age 45.

The analysis shows that rates of overweight and obesity are reaching pandemic proportions.

Berger’s findings suggest “an impending explosive increase in obesity‐associated cancers in young adults.”

The review is published in the journal Obesity.

Childhood obesity raises the risk of developing cancer at a younger age. But it also has long-term implications, increasing the risk of cancer later in life.

For example, adults who have been obese are at twice the risk of multiple myeloma compared to adults who haven’t been obese.

Losing the excess weight won’t completely wipe out the added risk. But it will cut it down some. Plus, it improves overall health.

Dr. Mark A. Ranalli, director of the embryonal tumor program in the divisions of hematology, oncology, and bone marrow transplantation at Nationwide Children’s Hospital in Ohio, reviewed the study.

He told Healthline that the gold standard for clinical investigations continues to be tightly controlled, prospective clinical trials.

Ranalli noted that Berger’s analysis is a retrospective study.

He explained that the subject population isn’t uniform regarding other factors, beyond obesity, that may contribute to cancer development.

“So, its conclusions still need to be regarded with caution. That said, I think its conclusions are in keeping with what previous animal and human research has suggested all along,” said Ranalli.

According to Berger, a young person with a BMI over 30 is more likely to have an aggressive cancer.

Obesity speeds up cancer progression in a number of ways.

It triggers the immune system to produce harmful byproducts that mutate DNA. Obesity also affects metabolism and intestine microbiota in ways that help cancer thrive.

Obesity can also have an effect on how one responds to treatment. It can lead to more complications and a poorer outlook.

When children and young adults get cancer, additional health problems can occur months or years after treatment ends, said Ranalli.

“The chance of having late effects increases over time as we see childhood cancer patients that survive longer and longer. Long-term risks are related to the diagnosis, type of surgery and chemotherapy used, the need for radiation, long-term immune modulatory drug use, and other factors,” he added.

Ranalli said cancer treatment in young patients can cause damage to the heart, lungs, or kidneys. It can affect development and fertility and increase the risk of second cancers. Social, psychological, and cognitive problems can also occur.

“To the extent that obese children and young adults are ‘less fit,’ they are poorer hosts with respect to their ability to tolerate treatments, particularly more aggressive treatments,” explained Ranalli.

“There are also issues with predictable drug distribution. There is some data to suggest that obese patients may fare more poorly in terms of overall survival for a given cancer diagnosis,” he said.

But losing excess weight can improve the outlook.

“Weight loss will make you more able to tolerate treatment if you do develop cancer. Weight loss will mitigate the effects of obesity on the heart, kidneys, musculoskeletal system, brain, and other organs,” said Ranalli.

Berger offered recommendations on breaking the link between obesity and cancer in young adults.

Documenting health data, including BMI, throughout life would help doctors monitor their patients better and guide cancer screening. He suggests that increased use of electronic medical records would help in that regard.

But he believes the most effective way to tackle the problem is by preventing obesity in the first place.

Statistics show we’re headed in the wrong direction.

According to the Centers for Disease Control and Prevention, childhood obesity has tripled in the United States since the 1970s. In 2015 to 2016, nearly 1 in 5 people aged 6 to 19 years were obese.

Worldwide, more than 124 million children and adolescents and 650 million adults were obese in 2016, according to the World Health Organization.

There are many contributing factors, including sedentary lifestyle and poor diet.

Ranalli said we shouldn’t be surprised by the increasing frequency of adult cancers in younger patients.

“Consider this frightening and sobering fact: The face of poverty has changed from the gaunt malnourished child to the obese one. Poorer children have less access to healthier (more expensive) foods and are forced to substitute cheaper fast food, snacks, and highly processed foods which are, among other things, higher in fats and lower in fiber — both well-known contributors to cancer progression,” he said.

“Obesity is a serious and pervasive problem that causes cumulative devastating and often irreversible injury. Its impact reaches far beyond what we historically felt was just a cardiovascular health problem,” said Ranalli.