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A new study suggests that people who wait until they are older to have sexual intercourse for the first time tend to have a lower risk of experiencing depression as adults. The research indicates that a substantial part of this reduced risk appears to be explained by higher educational achievement and greater household income. These findings were recently published in The Journal of Sexual Medicine.
Depression is a widespread mental health condition influenced by a mix of biological, environmental, and social elements. Economic hardship, including low household income and unemployment, is a known contributor to depressive symptoms. At the same time, genetics account for roughly thirty to forty percent of the risk for developing depression. This highlights how heavily our environments interact with our biology to shape mental wellness.
Researchers have recently begun looking at behavioral patterns to understand how they might shape mental health outcomes over a person’s lifespan. One specific behavior that has attracted attention in public health circles is the age at which a person first has sexual intercourse.
Previous research has hinted at an association between an early sexual debut and an increased risk of adult depression. Researchers suspect this connection might operate through a chain of life events. An early sexual initiation might influence a person’s educational path, economic stability, and social relationships, which eventually impact their mental health.
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Kaifa Tang and colleagues from Guizhou University of Traditional Chinese Medicine in China wanted to better understand exactly how this chain of events unfolds. They sought to determine whether the timing of a person’s first sexual experience genuinely alters depression risk, or if other underlying factors are responsible for the connection. To do this, the research team combined two distinct methods, analyzing both observational survey data and genetic data.
For the first part of their investigation, the researchers analyzed data from the National Health and Nutrition Examination Survey. This survey is an ongoing, nationally representative program designed to assess the health and nutritional status of adults and children in the United States. It combines interviews with physical examinations.
The team looked at records from 4,907 adult participants surveyed between 2013 and 2016. Roughly half of the participants were women. Participants self-reported the age at which they first had sexual intercourse as a specific numerical value. The survey also evaluated their depressive symptoms using a standard screening questionnaire.
In addition to sexual history and depression scores, the researchers collected data on various personal characteristics to ensure their analysis was accurate. These variables included age, sex, race, marital status, education level, and household income. They also tracked health behaviors and biological markers like smoking habits, alcohol intake, body mass index, and vitamin D levels.
When analyzing the survey data, the researchers found an inverse relationship between the age of first sexual intercourse and depression severity. People who reported having sex at older ages generally reported fewer depressive symptoms on the screening questionnaire.
This association was present in both men and women, but it was much stronger among the female participants. When the researchers adjusted their statistical models to account for differences in income, education, and health behaviors, the link between sexual timing and depression vanished for men. For women, however, the association persisted, even after accounting for these everyday variables.
The researchers also used a statistical tool to look for curved or non-linear patterns in the data. They found that depression scores steadily dropped as the age of first sexual intercourse increased up to about 17 years old. The depression scores leveled off around age 19 and a half, then rose slightly for those who waited even longer. This curved pattern persisted for women but not for men after accounting for socioeconomic factors.
To complement the survey data, Tang and colleagues conducted a second study using a statistical technique called Mendelian randomization. This method acts a bit like a natural experiment. It uses known genetic variations that are linked to a specific behavior or trait to see if that trait influences a specific health outcome.
Because a person’s genes are randomly assigned at birth, they are generally not influenced by the environmental factors and daily life choices that confuse observational studies. By looking at genetic markers associated with a later age of first sexual intercourse, the researchers could test if those same genes predicted a lower risk of depression later in life.
The team pooled genetic information from massive datasets known as genome-wide association studies. These studies scan the entire genetic code of hundreds of thousands of people to find tiny variations linked to specific traits. The researchers examined genetic predictors for the timing of first sexual intercourse, educational attainment, household income, smoking habits, and depression.
In the initial genetic analysis, the researchers found that genetic tendencies for a later sexual debut were associated with a lower risk of both general and severe depression. The genes linked to delaying sex were also associated with higher educational achievement, higher household income, and a lower likelihood of smoking.
Next, the researchers used advanced models to see what happened to the depression risk when they factored in the genetic predictors for these other life outcomes. When they accounted for genetically predicted household income, the direct association between the timing of first sex and depression almost completely disappeared for both men and women.
A similar drop occurred when the researchers adjusted for educational attainment. This suggests that much of the link between the timing of a person’s first sexual experience and depression runs through socioeconomic factors. Waiting to have sex is strongly associated with staying in school longer and earning more money, which in turn protects against depression. However, the timing of first sex did not lose all of its association in women. After adjusting for smoking, a weaker association with depression remained. For severe depression, the association stayed significant even after accounting for all of the mediating factors.
The researchers calculated how much of the effect was carried by these intermediary steps. They found that household income was a major mediator for both sexes when looking specifically at severe depression. For women in particular, the number of years spent in school acted as a primary mediator for the link between delaying sex and avoiding depression.
The genetic analysis also revealed a two-way street between these factors. Genetic predispositions for higher education and higher income were associated with delaying sexual debut. At the same time, a genetic tendency toward smoking was linked to having sex at an earlier age.
The researchers noted several limitations to their methodology. The genetic markers used to predict the timing of first sexual intercourse might actually represent broader behavioral or socioeconomic tendencies. A person’s genes might code for a general cautiousness or an orientation toward long-term planning, rather than just dictating when they first have sex.
The survey data from the first part of the study relied on participants accurately remembering and reporting their past behaviors. The genetic portion of the study relied mostly on data from individuals of European ancestry. Because genetic patterns can vary, these results might not apply to populations with different genetic backgrounds.
The stronger associations observed in women point to environmental contexts that the data could not measure. Social dynamics like coercion, unequal power relationships, and gender-based violence might influence both early sexual experiences and later mental health in women. Future research is needed to explore how these social contexts shape the differing results between men and women.
The study, “Consistent causal evidence from observation and genetics: socioeconomic mediators of the effect of sexual debut timing on depression,” was authored by Kaifa Tang, Bangwei Che, Hongyan Zhang, Jingju Yin, Jiancheng Zhai, An Yan, and Cen Lv.
