To date, the National Institute of Health has found evidence of 13 obesity-related cancers, but are there more?
Months ago, the Swedes released a teaser that they had found over 30 cancers with increased risk in persons living with obesity and overweight. Since then, I have been waiting for the study to drop, and it did this month in THE LANCET Regional Health Europe.
The currently known obesity-related cancers:
Below is the list of the 13 NIH obesity-related cancers in order of highest risk or lowest risk, with breast cancer separated into two categories. All of them have an increased risk of both being obese and overweight, with the exception of colorectal cancer, which only has a known risk in persons with obesity and not overweight. Several have a higher risk for persons with obesity over the elevated risk for persons with overweight. 1
endometrial (uterine)
esophageal adenocarcinoma
gastric cardia (stomach near the esophagus)
liver
kidney
pancreatic
meningioma (this tumor may be benign or cancerous)
gallbladder
colorectal
postmenopausal breast cancer
multiple myeloma
ovarian (risk goes up further with weight)
thyroid
premenopausal breast cancer
The Swedish Study
First, some definitions in the study. BMI ranges used are the same as those accepted in the US, with 18.5-24.9 kg/m2 as normal and ≥30 kg/m2 as obesity. With the analysis, BMI categories were in increments of 5mg/m2 as they are in the US. The study separated the cancers into cancers in men and cancers in women. The model is a Cox regression model meaning that it looks at the age and number of years that have passed for the outcome, meaning BMI was analysed in relation to cancer risk. The study further stratified subjects by birth year, height, mode of weight and height assessment, marital status, education level, smoking status, and birth country. With analysis, adjustments were made to height to remove this associated risk factor.*
The study also examined young people. At the start of the study, the mean age for men was 23.1 years, mean BMI was 22.5 kg/m2, and obesity was only 3% of the men. For women, the mean age was 31.3 years, mean BMI was 24.0 kg/m2, and obesity was only 9% of the women. The minimum age for study inclusion was 17 years. When data collection was suspect, such as a recalled weight, extreme weights/heights/BMIs, or prior cancer diagnosis, the individual was excluded. The study used computer analysis of chart data, only looking at individuals who did have a preexisting cancer diagnosis. A total of 4,142,349 individuals (2,129,149 men and 2,013,200 women) were analyzed.
The results were surprising in the number of cancer types that have not been previously associated with obesity. These include: oral cavity, nasal and paranasal sinuses, gastric (gastrointestinal stromal tumors), small intestine, biliary tract, pancreatic islets, adrenal glands, parathyroid gland, pituitary gland, connective tissue, lymphoid neoplasms, and myeloid neoplasms for both men and women, and also included cancers of the head and neck (adenocarcinoma), penis, and malignant melanoma for men, and cancers of the head and neck (squamous-cell carcinoma), nodular melanoma, vulva, and cervix (adenocarcinoma) for women.2 Sex was found to be a factor in cancers of the lip, tongue, head and neck adenocarcinoma, head and neck squamous-cell carcinoma, malignant melanoma, connective tissue, and lymphoid tissues.2 Impressively, the study looked at specific subtypes of cancers and found that only some subtypes have an increased risk. The subtypes found to have an increased risk were gastric gastrointestinal stromal tumors, small intestinal neuroendocrine tumors, cervical adenocarcinoma, diffuse large B-cell lymphoma in men, and nodular lymphocyte-predominant Hodgkin lymphoma.2
The above graphs are from the the study. 2
The Swedish study found that women with increased BMI are at potential risk for 16 not previously established cancers, and men with increased BMI were found to have an increased potential risk of 15 not previously established cancers. When combining the sexes, there were 18 not previously established cancers for which the risk is potentially increased with increasing BMI. When we add these 18 cancers to the previously known 13, this is 31 cancers that are potentially obesity-related.
It is too soon to know how the scientific community at large and in the US will use the Swedish study or if the National Institute of Health (NIH) will add more cancers to the list of having an increased risk in people with extra weight. Before being accepted, I suspect this study will be replicated in other countries and if the findings are the same, the 13 will have company.
*Adjusting results for height is important as tallness is strongly associated with 20 cancers.
2. Body mass index and risk of over 100 cancer forms and subtypes in 4.1 million individuals in Sweden: the Obesity and Disease Development Sweden (ODDS) pooled cohort study
Sun, Ming et al.
The Lancet Regional Health – Europe, Volume 45, 101034
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