Fundamental factors that influence puberty
Different research papers have found direct genetic effects to account for at least 46% of the variation of timing of puberty in well-nourished populations. The genetic relationship of timing is strongest between mothers and daughters. The specific genes affecting timing are unknown. Researchers have hypothesized that early puberty onset may be caused by certain hair care products containing estrogen or placenta, and by certain chemicals, which are use in making cosmetics, toys, and plastic food containers.
Genetic factors account for half of the variation of the timing of puberty, followed by environment factors, which are clearly important as well. Nutrition is the most important of the environmental influence. One of the foremost observed environmental effects is high altitude. But a number of others have been identified, all which affect timing of female puberty more clearly than male puberty.
Effects of hormone and steroids
Theories derived from research work and animal evidence show that environmental hormones and chemicals may affect aspects of prenatal (before birth) or postnatal (after birth) sexual development in humans. Huge amounts of incompletely metabolized estrogen and progesterone from pharmaceutical products are excreted into the sewage systems of big cities, and are sometimes noticeable in the environment. Excessive exposure of a child to hormones or other substances that activate estrogen or androgen receptors could induce some or all of the changes of puberty.
Conspicuous level of partial puberty from direct exposure of young children to small but significant amounts of pharmaceutical sex steroids from exposure at home may be detected during medical evaluation for precocious puberty (attainment of puberty earlier than normal).
BPA (Bisphenol A) is a chemical use in making plastics, and it is often use in making baby bottles, water bottles, sports equipment, medical devices, and as a coating in food and beverage cans. Medical scientist are concerned about BPA's behavioral effects on fetuses, infants, and children. Their current exposure levels can effect the prostate gland, mammary gland, and lead to early puberty in girls. BPA mimics and interferes with the action of estrogen, which is an important regulator of reproduction and development. It diffuses out of plastic into liquids and foods that may be consumed by children. The Centers for Disease Control and Prevention (CDC) found measurable amounts of BPA in the bodies of more than 90 percent of the U.S. population studied. The highest estimated daily intakes of BPA was found in infants and children.
Effect of nutritional factor
Nutritional factors are the most conspicuous and most powerful environmental factors affecting timing of puberty. Female children are especially sensitive to nutritional regulation because more often excess calories are reflected in the amount of their body fat, which signals to the brain the availability of resources for initiation of puberty.
For most of the last few centuries much evidence suggests that, nutritional differences accounted for bulk of variation of puberty timing in different populations. Today there is a global increase in the consumption of animal protein, better dieting, and increase in childhood obesity. This have resulted in falling ages of puberty, mainly in those populations with the higher preceding ages. Available dietary energy (simple calories) is the most important dietary influence on timing of puberty. The quality of the diet plays a major role as well. As occurred with typical vegetarian, lower protein intakes and higher dietary fiber intakes, are associated with later onset and slower progression of female puberty.
Effect of obesity
Medical scientists have connected early obesity with an earlier onset of puberty in females. Obesity have been cited as a cause of breast development before nine years and menarche (commencement of menstruation) before twelve years.
Effect of exercise
Especially in females, the average level of daily physical activity has also been observed to affect timing of puberty. Increase level of exercise, whether for athletic or body image purposes, or for daily subsistence, reduces body fat and energy calories available for reproduction and there by slows puberty. The effect of exercise is often amplified by a reduced body fat mass and cholesterol.
Effect of physical and mental illness
Obviously chronic diseases can delay puberty in both males and females. Those that interfere with nutrition have the strongest effect. Inflammatory bowel disease, chronic parasite infections and tuberculosis have been notorious for such an effect.
If mental illnesses occur in puberty. The brain undergoes considerable development by hormones which can contribute to mood disorders such as Major depressive disorder.
Effect of social and stress factors
Psychological and social factors are some of the least understood environmental influences on timing of puberty. They are the least in comparison with the effects of genetics, nutrition, and general health. Mechanisms of these social effects are unknown, though different types of physiological processes, including pheromones (chemical emission from an animal that has influence on the behavior or body chemistry of another animal of the same species) have been suggested based on animal research.
The family is the most important part of a child psychosocial environment. Social influence researchers have investigated features of family structure and function in relation to earlier or later female puberty. Most of the studies have reported that menarche may occur earlier in females in high-stress households, whose parent (fathers) are absent during their early childhood, who have a stepfather in the home, who are subjected to prolonged sexual harassment in childhood, or who are adopted from a developing country at a young age. Conversely, when a girl grows up in a large family with a biological father present, menarche may be slightly later.
Wartime with threat to physical survival is a more extreme degrees of environmental stress, that have been found to be associated with delay of maturation, an effect that may be compounded by poor nutrition.