The prevalence of obesity in adolescents has increased globally and is in line with the increasing incidence of cancer at a young age. There are even reports that obesity is a contributing factor to developing several types of cancer, replacing smoking as a major cancer factor.

Obesity in Adolescents Increases Cancer Risk



There are several studies on the relationship between obesity and the incidence of cancer and the resulting death by measuring and classifying the body mass index (BMI) of adolescents,



Obesity in Adolescents

Obesity is a medical condition in the form of an increase in the body's proportion in a category above the normal average value (BMI> 30). Generally, determining obesity can be through several anthropometric measurements, such as body mass index (BMI) and waist circumference.

Adolescent obesity has increased in prevalence worldwide since 1980. In 2016, an estimated 1.97 billion adults and 338 million children and adolescents worldwide were categorized as overweight (overweight to obese).

Obesity is a factor in many chronic diseases, such as cardiovascular disease, diabetes, and metabolic syndrome, reducing life expectancy. Additionally, overweight and obesity are also well suspected of increasing cancer risk as adults.



How obesity can trigger cancer

Excessive energy intake can cause fat accumulation in several parts of the body, such as the upper arms, hips, stomach, and thighs. In theory, adipose tissue, especially visceral fat, acts as an endocrine organ that actively secretes various proinflammatory adipokines. The increase in adipose tissue increases adipokine secretion and then increases free fatty acids that trigger insulin resistance and various other metabolic disorders related to obesity.

Visceral fat does not play a role in human energy metabolism. It can actively secrete hormones and adipocytokines, such as leptin, adiponectin, resistin, 1-Methylcyclopropene (MCP-1), and retinol-binding protein 4 (RBP4). Like TNF-α, RBP4 acts as an interleukin that increases chronic diseases' progression, including insulin resistance and chronic inflammation.

Increased inflammation markers can lead to tumor development (increased proliferation and survival of malignant cells, as occurs in angiogenesis). This mechanism is the basis for the notion that obesity can lead to cancer.

Another theory explains that obesity causes changes in biological mechanisms, namely: bioavailability and synthesis of steroid sex hormones, insulin resistance, the release of growth factors and/or proinflammatory cytokines, and energy expenditure irregularities that can lead to the progression of cancer cells.

There is a report that the association between obesity and cancer risk will increase if obesity is experienced in some types of malignancies, such as acute myeloid leukemia or myelodysplastic syndrome.



Scientific Evidence Regarding Association between Obesity in Adolescents and Cancer Risk

A meta-analysis study by the American Institute for Cancer Research looked at the association of obesity in general with the onset of cancer, ranging from measuring the amount of body fat in adolescents aged 18 years to the incidence of continued weight gain in adulthood.

This study mentioned that obesity, which starts in adolescence to adulthood, can increase the risk of oral, pharyngeal, esophageal, stomach (cardiac), pancreatic, bile, liver, colorectal, breast (postmenopausal), ovarian, endometrial cancer, prostate, and kidneys.

The long-term cohort study by Furer et al. studied 2,298,130 people, of which 928,110 were women, and 1,370,020 were men. Of the total participants, there were 55,841 cases of cancer. The mean age at diagnosis was 40 years.

This study found an increased risk of cancer types in men with a BMI over the 50th percentile as adolescents. The most common cancers found in men are Hodgkin's and non-Hodgkin's lymphoma, melanoma, and colorectal cancer.

However, most obesity cases were not associated with cancer incidence in women, apart from cervical cancer and breast cancer. The study results also showed a high BMI (overweight:> 85–95 percentile, obesity:> 95th percentile) correlates with an increased risk of cancer after ten years. Additionally, the increase in BMI was positively associated with an increase in mortality.

A prospective cohort study by Levi et al. examined 1,087,358 men and 707,212 women aged 16–19 years. After a mean follow-up of 23 years, they found that 551 participants were diagnosed with pancreatic cancer, 423 patients with cancer were male, and 128 were female.

Compared with the low to normal BMI group, a high BMI, namely overweight and obesity, is associated with pancreatic cancer risk. In men, a fairly robust analysis demonstrated that the higher the BMI stratification, the higher the risk of cancer, as indicated by normal-high BMI, overweight, then obesity.

Overall, pancreatic cancer caused by overweight and obesity in adolescents accounts for 13% of the Jewish Israeli population.

A case-controlled trial by Kim Kyoung-Nam et al. in Korea assessing the association between obesity in adolescents and papillary thyroid cancer incidence also yielded similar results. The study included 1,549 patients with papillary thyroid cancer and 15,490 individuals as controls. The participants' BMI was calculated when the participants were 18 years old.

The results showed that adolescents who had a BMI of ≥25 at the age of 18 years had a higher risk of developing papillary thyroid cancer as adults when compared with adolescents who had a BMI of ≤23 at the age of 18 years. Thus, it can be concluded that being overweight and obese as adolescents can increase the risk of developing papillary thyroid cancer in adulthood.



Overcoming Obesity in Adolescents

Prevention strategies generally focus on lifestyle interventions to prevent weight gain. It is considered very crucial to normalize body weight before puberty for several reasons.

Generally, children and adolescents who are obese will remain obese into adulthood. In addition to its association with the risk of many types of cancer, obesity in adolescents also significantly increases the risk of cardiovascular diseases, such as coronary heart disease; and metabolic disorders, such as diabetes mellitus in adulthood.


Recommendations regarding the Prevention of Obesity

According to the World Health Organization (WHO), obesity prevention needs to be done from five, even considered a top priority. WHO itself recommends several things to prevent obesity from the age of infants and toddlers, namely:
  • Promote exclusive breastfeeding of infants
  • Avoid adding added sugar in added formula milk.
  • Educate mothers to accept their children's ability to receive energy from the food they eat, rather than forcing children to finish all the food 
  • Ensuring the availability of micronutrient intake needed to support growth

Meanwhile, for children to adolescents, obesity prevention can be done by:
  • Promote an active lifestyle by modifying the environment that increases physical activity in both school and community. Doing physical activity (for example, walking every day) with an intensity of at least 1 hour/day. 
  • Limiting television viewing habits
  • Promote the habit of eating fruits and vegetables
  • Limiting the intake of high-calorie foods that have minimal micronutrients, such as packaged snacks
  • Limit your intake of soft drinks with added sugar or artificial sweeteners
  • Provide sufficient information and training for choosing healthy foods


Conclusion
As explained in the description above, obesity, especially in adolescents, increases cancer incidence. This condition is thought to occur due to increased inflammation-causing adipocytokines secreted by adipose tissue, increasing malignant cells' proliferation.

Types of cancer associated with obesity are known to have reached 12 types, including mouth, pharynx, larynx, esophagus, stomach, pancreas, bile, liver, colorectal, breast, ovary, endometrium, prostate, and kidney.

Therefore, it is necessary to prevent obesity in children and adolescents through early weight control by staying active and maintaining a healthy nutritional intake. Thus, it is hoped it can reduce the risk of cancer occurrence in the future.


References
1. Furer A, Afek A, Sommer A, et al. Adolescent obesity and midlife cancer risk: a population-based cohort study of 2·3 million adolescents in Israel. 2020; Downloaded from https://www.thelancet.com/journals/landia/article/PIIS2213-8587(20)30019-X/full-text.
2. Kazan M and Karaiti I. The Association between Obesity and Cancer. Endocrinology & Metabolic Syndrome. 2015; 4(4): p. 1-13. Downloaded from: https://www.longdom.org/open-access/the-association-between-obesity-and-cancer-2161-1017-1000196.pdf .
3. Kim K, Hwang Y, Kim KH, et al. Adolescent overweight and obesity and the risk of papillary thyroid cancer in adulthood: a large-scale case-control study. Sci Rep 10, 5000. 2020; Downloaded from https://www.nature.com/articles/s41598-020-59245-3.
4. Weihrauch-Blȕher S, Schwarz P, and Klusmann J. Childhood obesity: increased risk for cardiometabolic disease and cancer in adulthood. Metabolism. 2019; 92: p. 147-52. Downloaded from  https://www.metabolismjournal.com/article/S0026-0495(18)30255-5/fulltext.
5. WHO. Recommendations for preventing excess weight gain and obesity. Downloaded from https://www.who.int/dietphysicalactivity/publications/trs916/en/gsfao_obesity.pdf?ua=1.
6. World Cancer Research Fund/ American Institute for Cancer Research. Body Fatness and Weight Gain and The Risk of Cancer. 2018; Downloaded from https://www.wcrf.org/sites/default/files/Body-fatness-and-weight-gain_0.pdf.
7. Zohar L, Rottenberg Y, Twig G, et al. Adolescent overweight and obesity and the risk for pancreatic cancer among men and women: a nationwide study of 1.79 million Israeli adolescents. Cancer. 2019; 125(1): p. 118-26. Downloaded from: https://acsjournals.onlinelibrary.wiley.com/doi/full/10.1002/cncr.31764 .