In men, low testosterone levels lead to the accumulation of total and visceral fat mass, triggering a self-reinforcing cycle of complications that reduce the levels of this hormone. The mentioned effects of estrogen deficiency in the female sex can be eliminated by exogenous hormone replacement therapy 18, 20. In menopausal women, a decrease in estrogen levels increases total adipose tissue mass, reduces lean body mass 18 and results in the loss of subcutaneous fat with a simultaneous increase in its amount in the abdominal cavity 19. Moreover, it has been shown that binge eating is especially prevalent in the female sex and develops most often during adolescence, in combination with higher levels of estrogens 17. They cause weight gain, mainly by inhibiting the hormonal activity of the thyroid gland and modulating the hypothalamus 16. Research shows that estrogens promote the accumulation of subcutaneous fat not only in women, but also in men 13, 14, 15. The ability to effectively accumulate fat is an evident biological advantage for women due to the periods of pregnancy and lactation, which require high energy expenditure of the body 12. According to researchers, the factor that allows women to store fat more efficiently is estrogen. Women have more total fat which is deposited subcutaneously and in the gluteal/femoral regions, while men on average have less total body fat but more in the central/abdominal region 11. It is believed that gender-specific physiological mechanisms are responsible for the higher incidence of obesity in women than in men. Overweight and obesity arise as a result of excessive development of the fat mass in proportion to the fat-free body mass. Additionally, the frequency of this disease is gradually increasing 10. Obesity is a health problem with an epidemic status and the incidence of 15% for women and 11% for men 13% in the general population 10. On the other hand, on the basis of studies carried out in children aged 7–13 and repeated again after 4 years, slight but statistically significant changes of this indicator occurring in both sexes with age were less pronounced for the right hand, which is considered to be more sensitive to the influence of prenatal steroids 9. In other studies a significant increase in the mean 2D:4D values of the left hand was found in girls and boys between the ages of one and nine, while in the older age groups the changes turned out to be much smaller 6. Some authors did not demonstrate such changes 7, 8. So far, it has not been clearly established whether 2D:4D changes with age in humans. It has been estimated that the sexual dimorphism index for 2D:4D in adults is less than 5% 6. It is known that PT stimulates, while PE inhibits the growth of the fourth finger, therefore PT lowers and PE increases the size of 2D:4D and, as a result, it is on average lower in men than in women 2. Studies conducted in men also showed that genetically determined sensitivity to testosterone (polymorphism of the androgen receptor gene) is related to the digit ratio 5. Moreover, a negative correlation between the PT/PE ratio in amniotic waters in pregnant women and 2D:4D ratio in children has been demonstrated 3, 4. The influence of prenatal testosterone (PT) and prenatal estrogens (PE) on digit ratio supported in experimental studies conducted in mice 2. This indicator is determined in the prenatal period (between the 10th and 13th week of fetal life) under the influence of sex hormones 1. The 2D:4D ratio is the ratio of the length of the second (2D) to fourth (4D) finger of the hand. The rate of weight loss after bariatric surgery is independent of prenatal exposure to sex hormones. Moreover, it seems that the 2D:4D index (especially of the right hand) may be a useful factor in early prediction of the risk of developing excessive body weight in humans. This relationship indicates a new area of activity in the field of obesity prevention. We have found that the development of excessive body weight in men and women, and fat accumulation in the upper arms, thighs and lower legs in women with obesity (but not men) are associated with increased prenatal estrogen exposure. We tested 125 adults with obesity (BMI ≥ 30.0 kg/m 2), 125 adults with overweight (BMI 25.0–29.9 kg/m 2) and 153 persons with normal body weight (BMI < 25 kg/m 2) of both sexes. In the current study we investigated whether the 2D:4D index, as a marker of the prenatal hormonal environment, is associated with the development of overweight and obesity in adults, and whether is it correlated with the rate of weight loss in patients after bariatric surgery. Prenatal testosterone decreases and prenatal estrogens increase this index. ![]() 2D:4D finger length ratio is a proxy of prenatal sex hormone exposure.
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