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Approximately 13 million children and adolescents in the United States aged 2-19 years are obese and since 1980, obesity prevalence among children and adolescents has almost tripled.

According to the U.S. Centers for Disease Control and Prevention, obese children are more likely to have high blood pressure, high cholesterol, type 2 diabetes and breathing problems. The CDC also reported that obese children and adolescents have a greater risk of social and psychological problems, such as discrimination and poor self-esteem, which can continue into adulthood.

And now, to add to the growing list of risk factors, researchers have revealed that childhood obesity could be disrupting the timing of puberty and ultimately lead to a diminished ability to reproduce, especially in females.

"Either extreme of the spectrum, anorexia or obesity, can be associated with reproduction problems," said Patrick Chappell, an assistant professor of veterinary medicine at Oregon State University and an author of the recent report.  "The issue of so many humans being obese is very recent in evolutionary terms, and since nutritional status is important to reproduction, metabolic syndromes caused by obesity may profoundly affect reproductive capacity."

The analysis was published in Frontiers in Endocrinology.

Researchers say they are still learning more about the overall impact of obesity on the beginning of puberty and effects on the liver, pancreas and other endocrine glands.  But in general, puberty appears to be starting earlier in girls. It is being accelerated.

This may have several effects, scientists have found. One theory is an impact on kisspeptin, a recently characterized neurohormone necessary for reproduction. Normal secretions of this hormone may be disrupted by endocrine signals from fat that serve to communicate to the brain. Another possible effect on pubertal timing, and reproduction in general, is disruption of circadian clocks, which reflect the natural rhythms of night and day. Disrupted sleep-wake cycles can affect the secretion of hormones such as cortisol, testosterone, and insulin.

"Any disruption of circadian clocks throughout the body can cause a number of problems, and major changes in diet and metabolism can affect these cellular clocks," Chappell said. "Disruption of the clock through diet can even feed into a further disruption of normal metabolism, making the damage worse, as well as affecting sleep and reproduction."

Researchers say it now appears that an excess of fat can also be contributing to infertility rates and reproductive diseases.

Some studies in humans have found correlations between early puberty and the risk of reproductive cancers, adult-onset diabetes, and metabolic syndrome. Early onset puberty has also been associated with increased rates of depression and anxiety in girls, studies have found, as well as increased delinquent behavior, smoking and early sexual experiences in both girls and boys.

Other research has suggested that such problems can persist into adulthood, along with lower quality of life, higher rates of eating disorders, lower academic achievement and higher rates of substance abuse.

Researchers say additional studies are needed.