Link Between Body Fat and the Timing of Puberty

Abstract

Several recent studies suggest that the timing of the onset of puberty in girls has become earlier over the past 30 years, and there is strong evidence that the increasing rates of obesity in children over the same time period is a major factor. This article reviews studies from the United States that examined the age of menarche and the age of onset of breast development and pubic hair as a function of body mass index, which is a good surrogate measure of body fat. These studies are nearly all crosssectional, so many questions remain unanswered. However, at least several studies show that girls who have relatively higher body mass index are more likely to have earlier menses, as well as a relationship between body mass index and other measures of pubertal onset. The evidence published to date suggests that obesity may be causally related to earlier puberty in girls rather than that earlier puberty causes an increase in body fat. In contrast, few studies have found a link between body fat and earlier puberty in boys. A growing body of evidence from both rodent and human studies suggests that leptin may be the critical link between body fat and earlier puberty. Leptin-deficient mice and humans fail to enter puberty unless leptin is administered, and rodent studies indicate that very low levels of leptin stimulate gonadotropin secretion both at the hypothalamic and the pituitary level. Current evidence indicates that leptin appears to play a permissive role rather than act as the critical metabolic signal initiating puberty. The linkage between body fat and the reproductive axis in girls may have evolved in mammals as a mechanism for ensuring that pregnancy will not occur unless there are adequate fat stores to sustain both the mother and the growing fetus. HISTORICAL PERSPECTIVESRecords from several northern European countries, particularly Norway, Denmark, and Finland, document that the age of menarche, a convenient marker for the timing of puberty in girls, decreased from ϳ16 to 17 years during the 19th century to ϳ13 years by the middle of the 20th century. 1 In the United States, a decline from 14.75 years in 1877 to just under 13 years by the period of 1950 to 1970 has been reported. It has been widely assumed that improved health and nutrition associated with the coming of the Industrial Revolution were responsible for most if not all of that decline in the mean age of menarche. At the very least, these historical data suggest that the timing of puberty is not solely genetically determined but can be influenced by epigenetic factors. There have also been studies to suggest that obese girls tend to mature earlier than normal and that "thin" girls tend to mature later. For example, a significant delay in puberty and menarche is seen in girls who are very physically active and have markedly diminished body fat. 2 After reviewing longitudinal growth data for 181 normal girls, Frisch and Revelle 3 observed that the mean weight at menarche was constant at ϳ48 kg for girls who reached menarche before age 1...

Do Secular Trends in Skeletal Maturity Occur Equally in Both Sexes?

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Age at Menarche and Cardiometabolic Health: A Sibling Analysis in the Scottish Family Health Study

“…Whether childhood adiposity is the sole driver of the associations of age at menarche with cardiometabolic health and CVD events, related to its strong inverse relationship with age at menarche,41, 42 remains to be determined. A limited number of studies were able to adjust for childhood characteristics when studying the associations of age at menarche with cardiometabolic health 2, 4, 14.…”

Effect of Age, Duration of Exposure, and Dose of Atrazine on Sexual Maturation and the Luteinizing Hormone Surge in the Female Sprague–Dawley Rat

“…However, it is also known that length of time needed to reach sexual maturation is inversely proportional to body weight rather than to chronological age (Kennedy and Mitra, 1963; Odum et al., 2004). Delayed puberty in girls has been associated with reduced body fat (Kaplowitz, 2008) or small weight for gestational age at birth (Ibanez and de Zegher, 2006), whereas trends toward an increased prevalence of precocious puberty (Kaplowitz, 2006) have been associated with overnutrition (Burt Solorzano and McCartney, 2010). Early‐life nutritional effects have also been reported to alter puberty onset and reproductive function postpubertally (Chan et al., 2015).…”