A study of over 380,000 people, published today in the journal Nature Genetics, has identified gene variations that influence the age of puberty, first sexual intercourse and first birth.
It is known from earlier studies that first sexual intercourse at an early age is associated with adverse educational achievements, physical health and mental wellbeing, and previous studies have established the roles of socio-cultural factors, such as peer-pressure and parental attitudes and supervision. This study shows that genetic factors that act on biological mechanisms, such as the timing of childhood physical maturity and personality, also contribute to the timing of sexual behaviour, and in this cohort genetic factors accounted for around 25% of the variation in the age at which individuals first had sexual intercourse.
To identify the gene differences which influence timing of sexual behavioural, researchers at the Medical Research Council (MRC) Epidemiology Unit at the University of Cambridge analysed the genetic data of 59,357 men and 66,310 women aged between 40 and 69 years old who were part of UK Biobank*, a national study for health research.
This analysis identified 38 gene variants that were associated with age at first sexual intercourse. Several of these gene variants were associated with earlier puberty timing and higher body mass index, but others were located in or near genes previously implicated in estrogen signalling, brain development and neural connections, and their analysis uncovered associations with a range of reproductive behaviours, such as age at first birth and number of children.
Dr John Perry, a senior investigator scientist at the MRC Epidemiology Unit, and a lead author of the paper, said:
While social and cultural factors are clearly relevant, we show that age at first sexual intercourse is also influenced by genes which act on the timing of childhood physical maturity and by genes which contribute to our natural differences in personality types.
One example is a genetic variant in CADM2, a gene that controls brain cell connections and brain activity, which we found was associated with a greater likelihood of having a risk-taking personality, and with an earlier age at first sexual intercourse and higher lifetime number of children.”
In previous studies by the same team, it was found that an earlier age at puberty is linked to increased long-term risks for diseases such as diabetes, heart disease and some cancers.
Dr Ken Ong, a paediatrician and programme leader at the MRC Epidemiology Unit, and a lead author on the paper, added:
We have already shown that early puberty and rapid childhood growth adversely affect disease risks in later life, but we have now shown that the same factors can have a negative effect at a much younger age, including earlier sexual intercourse and poorer education attainment.
The investigators hope that future preventive efforts to delay puberty in young children, for example by avoiding excess childhood weight gain, will have benefits both on reducing adolescent risk-taking behaviours and for their future health as adults.
The research was funded by the MRC.
* UK Biobank recruited 500,000 people aged between 40-69 years in 2006-2010 from across the UK. Participants have undergone measures, provided blood, urine and saliva samples for future analysis, detailed information about themselves and agreed to have their health followed.
Felix R. Day, Hannes Helgason, Daniel I. Chasman, Lynda M. Rose, Po-Ru Loh, Robert A. Scott, Agnar Helgason, Augustine Kong, Gisli Masson, Olafur Th. Magnusson, Daniel Gudbjartsson, Unnur Thorsteinsdottir, Julie E. Buring, Paul M. Ridker, Patrick Sulem, Kari Stefansson, Ken K. Ong, John R.B. Perry “Physical and neuro-behavioural determinants of reproductive onset and success”. Nature Genetics. Published online 18 April 2016.