Men who were overweight as teens are more likely to develop up to 17 different cancers even if they later reach a healthy weight.
And although the study was only carried out on men, researchers believe the same applies to obesity in girls under 18.
An unhealthy teenage weight appeared to explain 15 to 25 percent of abdominal cancers in the Swedish research.
Men who were obese at 18 years old were three or four times more likely to go on to develop the disease.
The team expect that in three decades time, 32 percent of stomach cancer cases will be due to being overweight as a youngster.
In the same period, teenage obesity is projected to cause a total of 37 percent of esophagus cancer incidences, also considered an abdominal cancer.
Researchers at the University of Gothenburg, Sweden, attempted to map how the youth obesity epidemic could impact cancer trends over the next 30 years.
They found the alarming number of overweight teenagers could increase cancer diagnoses and cancer deaths the coming decades.
In the USA, over half of the stomach and esophagus cancer cases could be linked to a high teenage BMI, given how many American youngsters are currently overweight or obese.
Writing in the journal Obesity, the experts said we may even need to be stricter on what clinicians consider a healthy BMI for teenagers.
A “normal” BMI was found to elevate the risk of nine cancers, suggesting a healthy weight might be “lower” than previously thought.
Dr. Aron Onerup, of University of Gothenburg and St. Jude Children’s Research Hospital in Memphis, Tenn., said: “Overweight and obesity at a young age seems to increase the risk of developing cancer, and we see links between unhealthy weight and cancer in almost every organ.
“Given the alarming trend of obesity in childhood and adolescence, this study reinforces the need to deploy strong resources to reverse this trend.”
The team analyzed BMI’s impact on cancer risk among young men who were forced into military conscription in Sweden at the age of 18, between 1968 and 2005.
The cohort were found to have an increased chance of suffering cancer in the neck, brain, thyroid, esophageal, stomach, pancreatic, liver, colon, rectal, kidney, and bladder cancer.
With a high BMI as a teen, they were also more likely to develop malignant melanoma, leukemia, myeloma, and Hodgkin’s and non-Hodgkin’s lymphoma.
BMI particularly impacted abdominal cancers.
Obese 18-year-olds were three to four times more likely to develop cancer of the esophagus, stomach, and kidney.
The team went on to warn that those who were overweight or obese during the study were two to three times more likely to die within five years of being diagnosed with skin cancer, Hodgkin’s lymphoma and thyroid, bladder, and prostate cancer.
The same group had a 1.4 to two times higher chance of dying from cancers of the head and neck, rectum, and kidneys.
For several cancer types a BMI of just 20 to 22.4 elevated the risk – the normal BMI range is 18.5 to 24.9.
This included cancers head and neck, esophagus, stomach, pancreas, liver, and kidney, as well as malignant melanoma and non-Hodgkin’s lymphoma.
Professor of family medicine at University of Gothenburg, Maria Åberg, said this could mean young people should have a lower BMI than what is currently recommended.
She said: “This suggests that the current definition of normal weight may be applicable primarily for older adults, while an optimal weight as a young adult is likely to be in a lower range.
“Our research group has drawn similar conclusions regarding BMI in early adulthood and later cardiovascular disease.”
Prostate cancer was the only type that was more common among those who were not overweight or obese when they enlisted in the military.
The team suspected this is because men with a standard BMI are more likely to seek help for prostate problems, leading to earlier diagnoses.
Over the course of the study, 1,489,115 men were analyzed and 84,621 diagnosed with some form of cancer during the follow-up period.
Produced in association with SWNS Talker