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Bone Growth and Weight Gain
In females, approximately 50% of lifetime total body calcium is deposited into bones during puberty. In males, 50%-65% of lifetime total body calcium is laid down, with males having approximately 50% more total body calcium than females. A woman's maximal calcium deposition in bones occurs during the first half of puberty. Studies have also demonstrated that both genders first experience an increase in bone width followed by mineralization with calcium. Such a disparity between increase in size of bone and strength of bone may explain an increase in bone fractures during adolescence. The importance of calcium intake via dairy products and other sources to maximize bone calcification must be underscored to teenagers, some of whom may adopt fad diets or weight-loss regimens.
Both genders gain weight due to somatic growth and bone mineralization as described above. Early pubertal changes in boys demonstrate a reduction of fat mass which is followed during the last one-third of puberty by an acquisition of muscle mass. In adolescent girls, the majority of weight gain is due to fat accumulation, commonly distributed in the breasts, upper arms, back, and thighs. Anticipatory guidance regarding these predictable changes is important psychologically for many teenagers to have realistic expectations.
Genetic contribution to onset of puberty
A large national study compared the age at menarche in the 1960s to the period from 1999 to 2002. Overall, an earlier age of pubertal onset of 4.9 months was documented. Some intriguing research is indicating such advancement may be partially due to excessive weight gain. Speculation regarding the possible role of cattle and poultry feed/hormone supplementation also exists. Different racial groups also demonstrate different times for the onset of puberty (African-American girls at 8.9 years of age vs. Caucasian girls at 10 years of age). Large studies of Hispanic and Asian girls are incomplete. Most recent research has isolated several genes (LIN28B and GPR54) that seem to have important regulatory roles in the age of menarche and onset of puberty, respectively.
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