- Early puberty in girls is associated with obesity in adulthood.
- Genetic variants are used to study the link between early puberty and increase in Body Mass Index (BMI) .
- Mendelian Randomization - a statistical technique was used to study the relationship
Early puberty in girls is associated with obesity in adulthood, finds a study conducted at Imperial College London. The findings of the study are published in the International Journal of Obesity
.Previous studies have shown that there is a strong link between the onset of puberty and a woman's body mass in adulthood.
However, these findings are observational and can be influenced by certain factors like ethnicity, education level, diet and economic background. These factors make it difficult to determine whether early puberty is the cause for obesity.
‘Early puberty is associated with increase in Body Mass Index (BMI)’
Latest studies have proved that early puberty is a risk factor for overweight; girls who have their first period earlier are likely to have a higher Body Mass Index (BMI).
Dr Dipender Gill, a Wellcome Trust Clinical Research Fellow in the School of Public Health and first author of the study, said: "Previous studies have shown there is an association, but we didn't know whether early puberty caused obesity in adulthood, or was simply associated with it. In our latest study we've generated evidence to support that it is a causal effect."
In the study scientists used genetic variants as a tool to see the effect of the onset of puberty which is also known as age at menarche.
The genes in an individual's body are derived from their parents when the sperm and egg fuse to form an embryo. The embryo contains various genes which determine everything from hair color to risk of any disease.
A small change in the DNA sequence will alter its function. In terms of disease risk, single letter variants called single-nucleotide polymorphisms (SNPs) can result in a small increase or decrease in risk. The combination of variants of more than 20,000 genes contribute towards cumulative genetic risk.
Mendelian Randomization is a statistical technique that was used for the study. It uses genetic variants to study the relationship between early puberty and increase in BMI. The data of 182,416 women was used for the study and they identified 122 genetic variants that were significantly associated with the onset of puberty.
Then team gathered data from the UK biobank, which contains the biomedical information and genetic sequence of various people. They analyzed the data of about 80,465 women to see the effect of genetic variants that were related to early puberty and BMI.
Initial analysis revealed that there is a link between genetic variants and BMI, women who had variants related to early puberty had increased BMI. The scientists then tested another group of 70,692 women and found the same association.
According to Dr Gill, some genetic variants are linked to early puberty and some with later onset. With the help of these genetic variants the scientists were able to study the association between age at menarche and BMI in adulthood.
"We're not saying that it's a genetic effect, but rather that by using these genetic variants as a proxy for earlier puberty, we are able to show the effect of earlier puberty without the impact of external factors that might confound our analysis. We performed a range of statistical sensitivity analyses to test the robustness of our findings and they remained strong through this, so within the limitations of the study design, we are confident of findings."
Previously the researchers used the same technique to show that low iron levels are associated with an increased risk of heart diseases. Mendelian Randomization technique can also be used to study the relation between genetic variants and drug targets for cardiovascular disease and stroke.
The technique has certain disadvantages; it is possible that the genetic variants can influence BMI independently by altering metabolism or fat production.
According to researchers, it is still not clear how early puberty affects bodyweight. They also indicate that physical and emotional maturity may be linked to obesity.
Another finding is that the physical changes that occur during puberty, like increased fat deposit in breast tissue when established earlier can increase the risk of obesity in adulthood.
"It is difficult to say that changing someone's age of puberty will affect their adult risk of obesity and whether it is something that we can clinically apply - as it would unlikely be ethically appropriate to accelerate or delay the rate of puberty to affect BMI," added Dr Gill. "But it is useful for us to be aware that it's a causal factor- girls who reach puberty earlier may be more likely to be overweight when they are older."
Obesity in general means too much of body fat. Obesity occurs due to various reasons like; eating high calorie food, lack of sleep, lack of exercise, medications and improper metabolism. Obesity increases the risk of various diseases like diabetes, CVD, stroke, gall-bladder disease, infertility, high blood pressure and arthritis. It can be treated by doing regular exercise, change in lifestyle and by performing surgeries like bariatric surgery.
- Dipender Gill, Christopher F. Brewer, Fabiola Del Greco M, Prasanthi Sivakumaran, Jack Bowden, Nuala A. Sheehan & Cosetta Minelli. Age at menarche and adult body mass index: a Mendelian randomization study International Journal of Obesity (2018)