New research provides evidence that the genetic makeup of one’s romantic partner influences a person’s behaviors and health outcomes. The results, published in Behavioral Geneticspoint out that changes in your own weight, smoking habits, or alcohol consumption over time can be a result of your partner’s genetic predispositions.
The researchers conducted this study to investigate how a person’s partner can affect their health. Their aim was to explore the concept of social genetic effects, which refers to the influence of genetic factors in one’s environment, such as the genotype of their partner, on their own phenotype (observable traits or characteristics).
“I was mainly interested in exploring the combination of social science and genetics,” explained study author Kasper Otten from Utrecht University. “Behavior is clearly partly influenced by genetics, but much of the social sciences do not deal with this biological fact.
“In other words, if you combine the evidence in the social sciences of social influence on behaviors among partners with the knowledge that behavior has a genetic component, you get the interesting implication that your partner’s genes should also be important for one’s own behavior.”
To conduct the study, the researchers used longitudinal data from two large-scale studies: the Health and Retirement Study (HRS) in the United States and the English Longitudinal Study of Aging (ELSA) in England. These studies followed a nationally representative sample of adults aged 50 and over every two years, collecting data on health behaviors and outcomes. The HRS sample collected data from 1992 to 2018, and the ELSA sample collected data from 2002 to 2019.
Importantly, if a participant had a romantic partner, their partner was also invited to participate. Both studies also collected DNA samples, which allowed the researchers to examine the genetic profiles of the participants.
The researchers focused on three health outcomes: body mass index (BMI), smoking (cigarettes per day), and alcohol consumption (drinks per week). They used polygenic indices (PGIs) to measure genetic predisposition for these outcomes. PGIs aggregate many small genetic effects across the genome to predict an individual’s phenotype.
In the analysis of BMI, the researchers analyzed 59,325 observations from 9,522 individuals in 5,879 couples in the HRS, and 11,728 observations from 4,311 individuals in 2,729 couples in the ELSA. For drinks per week, they analyzed 52,023 observations from 9,140 people in 5,584 couples in the HRS, and 24,179 observations from 4,911 people in 3,264 couples in the ELSA. For smoking, they analyzed 60,029 observations from 9,546 individuals in 5,885 couples in the HRS, and 25,740 observations from 4,943 individuals in 3,311 couples in the ELSA.
The researchers found limited genetic similarity between partners for BMI, drinking and smoking behaviors. But the researchers observed strong social genetic effects, showing that their partner’s genotype influenced a person’s behaviors and health outcomes. Specifically, individuals were more likely to have a higher BMI, drink more, and smoke more if their partners had higher polygenic indices associated with these behaviors.
In other words, if someone’s partner had genes associated with higher body weight, they were more likely to have a higher body mass index (BMI) themselves. Likewise, if their partner had genes linked to increased drinking or smoking, they were more likely to adopt those behaviors as well.
These social genetic effects were not as strong as one’s own genetic makeup, but were comparable to the effects of education on health behaviors.
“It’s clear that genes act not only on individuals, but also on the people around us,” Otten told PsyPost. “This means that your behavior is not only influenced by your own genes, but also by the genes of those around you. Such social genetic effects have been widely established in some animals, but the evidence for humans has so far been limited.”
“We showed evidence of social genetic effects in health behaviors and outcomes—alcohol consumption, smoking, and body mass index—but in principle any behavior that is genetically influenced and subject to social influence can result in social genetic effects.”
The findings highlight the importance of considering a partner’s genetic influence when studying health behaviors and the couple’s environment. Understanding social genetic effects can have implications for health interventions and prevention programs, as well as identifying individuals who may be more susceptible to partner influence.
However, like all research, the study had some limitations. The samples were mostly older adults, and the results may not fully generalize to younger populations. Furthermore, the study only included individuals of European origin.
The study, “Partners in Health: Investigating Social Genetic Effects among Married and Cohabiting Couples,” wrote Kasper Otten and Jornt J Mandemakers.