TORONTO -- A specific receptor in the brain may explain why humans are growing taller and reaching puberty at an earlier age, according to new research.
In a study, on Wednesday, academics from the University of Cambridge in the U.K., as well as teams from several other universities in the U.K. and the U.S., said average height increased by about 10 cm in the U.K., and up to 20 cm in other countries during the 20th century.
And although scientists have long suggested this evolution could be related to humans enjoying more reliable access to food for pregnant women and children, the process in which the body senses its state of nutrition and turns that information into growth and sexual maturation has been unclear.
That is, until now.
It鈥檚 already known that food sends signals, such as the hormones leptin, which is produced in fat cells, and insulin, which is created in response to increases in blood sugar, to a part of the brain called the hypothalamus to indicate the body鈥檚 nutritional state.
These hormones act on a small group of neurons that produce signals called melanocortins, which act on a variety of receptors, two of which are present in the brain.
The first one, which is known as the melanocortin 4 receptor (MC4R), has previously been shown to regulate appetite and a lack of the receptor can result in obesity.
Now, as shown in this latest study, the role of the brain鈥檚 other melanocortin receptor, known as the melanocortin 3 receptor (MC3R), has been revealed.
According to the researchers, the MC3R system controls the release of key hormones involved in regulating growth and sexual maturation.
To arrive at this finding, scientists searched through the genetic information of half a million volunteers that is stored in the U.K. Biobank 鈥� a large database of genetic and health information 鈥� to find people with naturally occurring genetic mutations that disrupt the function of the MC3R.
They managed to identify a few thousand people with these various mutations and discovered they were, on average, shorter and entered puberty later than those without the mutations. These people also had lower amounts of lean tissues, such as muscle, although the mutations had no influence on how much fat they carried.
To test this theory in children, the researchers also studied nearly 6,000 participants from the Avon Longitudinal Study of Parents and Children (ALSPAC), a cohort study of children born in the former county of Avon, England during 1991 and 1992.
They found six children with mutations in MC3R and they were all shorter and had a lower lean mass and weight throughout childhood than their peers, which shows the effect of the mutations starts early in life.
What鈥檚 more, the researchers said they found one person who had mutations in both copies of the gene for MC3R, which is extremely rare. This person was 鈥渧ery short鈥� and entered puberty at the age of 20, according to the study.
鈥淭his discovery shows how the brain can sense nutrients and interpret this to make subconscious decisions that influence our growth and sexual development,鈥� Sir Stephen O鈥橰ahilly, a senior author on the study and director of the MRC Metabolic Diseases Unit at the University of Cambridge, said in a press release.
鈥淚dentifying the pathway in the brain whereby nutrition turns into growth and puberty explains a global phenomenon of increasing height and decreasing age at puberty that has puzzled scientists for a century.鈥�
O鈥橰ahilly added that their findings have 鈥渋mmediate practical implications鈥� for testing children with serious delays in growth and development for mutations in the MC3R.
鈥淭his research may have wider implications beyond child development and reproductive health. Many chronic diseases are associated with the loss of lean mass, including muscle, with resultant frailty,鈥� O鈥橰ahilly said.
鈥淭he finding that the activity of the MC3R pathway influences the amount of lean mass carried by a person suggests that future research should investigate if drugs that selectively activate the MC3R might help redirect calories into muscle and other lean tissues with the prospect of improving the physical functional of such patients.鈥�
