In a recent study published in Obesity, researchers evaluated the associations between body mass index (BMI) among young males and new-onset site-specific tumors to estimate population-attributable fractions (PAFs) due to BMI according to the projected prevalence of obesity.
Study: Associations between BMI in youth and site-specific cancer in men—A cohort study with register linkage. Image Credit: oatawa/Shutterstock.com
Background
The International Agency on Research on Cancer (IARC) has linked obesity to tumors of the esophagus, gastric cardia, colon and rectum, liver, gallbladder, pancreas, kidney, thyroid, and multiple myeloma in males.
However, the evidence of the associations among adolescents and young adults is limited, while it is typically consistent with the findings in older individuals. Further investigations could inform obesity prevention and management across ages.
About the study
In the population-based cohort study, researchers assessed the relationships between body mass index and location-specific tumor incidence among young males, accounting for cardiorespiratory fitness (CRF) and smoking status.
They also determined tumor site-specific PAFs of obese and overweight males based on past and current prevalences of obesity and overweight in Swedish and United States (US) youth.
Weight and height were assessed at 18 years of age in the Swedish national-level observational study to calculate BMI, and people were categorized as underweight (less than 18.5 kg per m2), overweight (between 25 and 29.9 kg per m2), or obese (equal to or greater than 30 kg per m2).
From 1968 until 2005, male participants aged 16 to 25 attended the conscription examination. Individuals who were diagnosed with tumors before or within five years of military conscription and died or emigrated within five years of conscription were excluded.
The Swedish Military service conscription record was used to identify conscripts. Tumor diagnostic data were acquired from Sweden's national patient registry and the mortality cause register. The International Classification of Diseases, eighth, ninth, and tenth revisions (ICD-8, 9, and 10) codes were used to designate site-specific tumors.
At conscription, CRF data were evaluated as the maximal aerobic exertion on cycle ergometer testing. Participants in the study were tracked until they were diagnosed with a tumor, died, emigrated for the first time after conscription, or the study terminated on 31 December 2019, whichever occurred first.
Cox proportional hazards regression modeling was used to calculate the hazard ratios (HRs) for the linear relationships for BMI, with age, year, conscription location, and parental educational level as variables.
Furthermore, sensitivity analyses were performed to investigate confounding factors such as cardiorespiratory fitness and smoking status. In addition, an ad hoc sensitivity analysis was performed to evaluate the impact of cognitive state on the results.
Results
The primary analysis comprised 1,489, 115 males; the mean participant age at recruitment was 18 years, and the mean BMI was 22, with two percent of individuals having a BMI of 30 or higher.
Obesity gradually increased with time, from one percent between 1968 and 1979 to four percent between 1990 and 2005, with a declining prevalence of body mass index below 20, a growing prevalence of body mass index 25 and higher, and a steady prevalence of body mass index between 20 and 24.9.
Obese males showed a higher likelihood of having hypertension, worse cognitive capacity, and less educated parents than their peers. Underweight and obese males showed a higher likelihood of smoking and had inferior cardiorespiratory fitness than their normal-weight peers.
During a 31-year follow-up (mean), 78,217 individuals developed tumors. The mean participant age at tumor diagnosis ranged from 39 years (Hodgkin lymphoma) to 59 years (prostate tumors).
BMI showed linear associations with the site-specific tumor incidence for all 18 tumors assessed (leukemia; malignant melanoma; Hodgkin lymphoma; myeloma; non-Hodgkin-type lymphoma; and tumors in the head and neck, lungs, thyroid, central nervous system (CNS), stomach, esophagus, liver, gallbladder, pancreas, rectum, colon, bladder, and kidney), in a few cases evident at body mass index values usually denoting normal-range weight (between 20 and 25 kg per m2).
A greater BMI was connected to a reduced prostate tumor risk. A few gastrointestinal malignancies have the highest HRs and PAFs.
Smoking was linked to a decreased prostate tumor and malignant melanoma risk but a greater risk of tumors in various locations, including the head and neck, esophagus, lungs, pancreas, stomach, liver, urinary bladder, and gallbladder. Adjusting for cardiorespiratory fitness, the connections between body mass index and tumor risk were increased.
After CRF adjustment, the most severe confounding by cardiorespiratory fitness was identified for lung tumors in underweight males. The HR values for obesity and overweight increased for several tumor sites, particularly gastrointestinal malignancies.
Elevated BMI was related to a greater risk of tumors in males with low CRF for tumors in many locations, including the head and neck, stomach, esophagus, liver, urinary bladder, kidney, colon, as well as Hodgkin lymphoma, in analyses stratified by CRF status at conscription.
The link between body mass index and tumors in the central nervous system, pancreas, thyroid, and leukemia was more robust among men with moderate to high CRF than in those with low cardiorespiratory fitness.
Cognitive capacity and muscular strength adjustments at conscription did not influence the findings. Based on present and historical prevalences of juvenile obesity and overweight in the US and Sweden, the PAF for gastrointestinal tumor locations was the greatest.
Conclusion
Overall, the study findings supported IARC-reported links between greater BMI in adulthood and a higher risk of site-specific malignancies, including tumors in several organs, and demonstrated that these relationships were independent of CRF.
Furthermore, the study found a link between childhood BMI and the chance of acquiring leukemia, myeloma, Hodgkin lymphoma, non-Hodgkin lymphoma, and tumors in the pulmonary tissues, urinary bladder, and the CNS.
The findings include PAF estimates that take into consideration the worldwide obesity pandemic. In case present trends continue, immediate action should be required to combat the obesity pandemic and prepare the healthcare system for an increase in tumor cases.
The complex relationship between obesity and male reproductive function