General, central obesities linked to higher risk of colorectal cancer

Sub: Science and tech

Sec: Health

Tag: Obesity

Context:

In India, a 2022 study in The Lancet estimated the percentage of obese women and men to be 9.8% and 5.4% respectively.

More on news:

Along with higher risk of heart disease and diabetes, obesity has been linked to a higher susceptibility to colorectal cancer (CRC), among others.

What is colorectal cancer (CRC)?

CRC refers to cancers of the colon or the rectum.
Colon cancer is sometimes called colorectal cancer.
This term combines colon cancer and rectal cancer, which begins in the rectum
The CRC incidence is relatively low in India.
Percentage of people who are alive five years after a CRC diagnosis is reportedly under 40% i.e. one of the lowest in the world.
CRC patients in India are generally young and present more frequently with advanced stages of the disease.

What is Obesity?

Obesity is a complex, chronic disease with several causes that lead to excessive body fat and sometimes, poor health.
Obesity is generally defined with the body mass index (BMI), a number that accounts for the height and the weight of the individual.
The BMI measures average body weight against average body height.

Body mass index (BMI) is a medical screening tool that measures the ratio of your height to your weight to estimate the amount of body fat you have.
Healthcare providers calculate BMI by using weight in kilograms (kg) divided by the square of height in meters (m2)

What are the three types of obesity?

Healthcare providers classify obesity into class types based on how severe it is.
They use BMI to do it.
- They include:
- Class I obesity: BMI 30 to <35 kg/m².
- Class II obesity: BMI 35 to <40 kg/m².
- Class III obesity: BMI 40+ kg/m².

Which groups are at risk of colorectal cancer?

Scientists began by analyzing the BMI, weight, height, waist circumference, hip circumference, and the waist-to-hip ratio of more than 3 lakh people to group them into four body shapes based on their observable characteristics: PC1, PC2, PC3, and PC4.
PC1 individuals were “generally obese”, while PC2 included tall individuals with a low waist-to-hip ratio.
PC3 included tall individuals with central obesity, with excess fat deposited around the abdomen.
PC4 had those who had an athletic body shape.
PC1 and PC3 individuals were strongly correlated with higher CRC risk while PC2 and PC4 were not associated with CRC risk.
These associations were also linked to the site at which CRC occurred and the sex of the individual.

How genes are responsible for obesity?

Using a technique called genome-wide association study (GWAS), the researchers looked for small variations in the DNA.
GWAS is used to find correlations between gene variations and traits in large groups of people.
Variation in a gene called AKT was implicated in the higher CRC risk for PC1 individuals.
AKT regulates cell survival, insulin signaling, and the formation of blood vessels and tumors in humans.
Variation of the RAF1 gene was found to be implicated in PC3 individuals’ CRC risk.
RAF1 mediates, among other processes, the transformation of normal cells into cancerous cells.
Genetic variations associated with risk for PC1 individuals were most highly expressed in the brain and in the pituitary gland.
- The pituitary gland is located as the base of the brain and produces hormones important for regulating growth, blood pressure, and functions of the sex organs, the thyroid glands, and the kidneys.
Variations associated with risk in PC3 individuals were found enriched in adipose tissue, nerve, cervix uteri, uterus, blood vessel, breast, fallopian tube, and ovary.
Genetic variations found in the GWAS analysis of PC1 and PC3 were “positively associated” with CRC risk.

Terms in news:

Genome-wide association study (abbreviated GWAS):

A genome-wide association study (abbreviated GWAS) is a research approach used to identify genomic variants that are statistically associated with a risk for a disease or a particular trait. The method involves surveying the genomes of many people, looking for genomic variants that occur more frequently in those with a specific disease or trait compared to those without the disease or trait.

Mendelian randomisation test:

Mendelian randomization can be used to look at whether levels of a substance found naturally in a person’s body is linked to disease. Measuring the levels themselves can be a problem because the levels can change in response to other factors that could be related to the disease, such as diet, smoking, or alcohol use.

Modern Genetics:

Modern genetics is founded on the classical study of seven genes by Gregor Mendel, even though until relatively recently little was known about their function.
Modern genetics focuses on the chemical substance that genes are made of, called deoxyribonucleic acid, or DNA, and the ways in which it affects the chemical reactions that constitute the living processes within the cell.