Japan: Lack of sexual interest is a risk factor for all-cause mortality in men

Sakurada K, Konta T, Murakami N, Kosugi N, Saito T, Watanabe M, et al. (2022) Association between lack of sexual interest and all-cause mortality in a Japanese general population: The Yamagata prospective observational study. PLoS ONE 17(12): e0277967, Dec 14 2022. https://doi.org/10.1371/journal.pone.0277967

Abstract
Background: Sexual interest is essential for maintaining positive sexual relationships and sexual function, which have recently been recognized as important indicators of good health and quality of life. Here, we prospectively investigated associations between sexual interest and mortality in a community-based population.

Methods: This study enrolled 20,969 subjects (8,558 males and 12,411 females) aged ≥ 40 years who participated in annual health check-ups in Yamagata Prefecture. Sexual interest was assessed by a self-report questionnaire. Associations between sexual interest and increased all-cause mortality, cardiovascular disease mortality, and cancer mortality were investigated by Cox proportional hazards modeling.

Results: During follow-up (median: 7.1 years), 503 subjects died; 67 deaths were due to cardiovascular disease, and 162 were due to cancer. Kaplan-Meier analysis showed that all-cause mortality and cancer mortality were significantly elevated among men who lacked sexual interest (log-rank P<0.0001, P<0.05). Cox proportional hazards model analysis with adjustment for age, hypertension, diabetes, dyslipidemia, smoking, alcohol drinking status, BMI, education, marital status, frequency of laughter, and psychological distress showed that the risk of all-cause mortality was significantly higher among men who lacked sexual interest than men who had sexual interest (hazard ratio [HR] 1.69; 95% confidence interval [CI], 1.17–2.44).

Conclusion: Lack of sexual interest is suggested to be a risk factor for all-cause mortality in Japanese males over 40 years old. This finding has implications for the importance of sexual interest in increasing longevity in this population.

Discussion

Although sexual activity and sexual satisfaction are considered of benefit to psychological health and wellbeing in older groups, the association between sexual interest and longevity has not been investigated. This study is the first to prospectively examine associations between sexual interest and all-cause mortality, and cardiovascular and cancer mortality in a community-based population.

In our sample of people aged 40 years or more, 8.3% of males and 16.1% of females indicated a lack of sexual interest. Similar results were reported by Lindau et al. in two cross-sectional population-based surveys of aging conducted in the US [4]. Baseline characteristics indicated that a lack of sexual interest was associated with greater age, higher prevalence of past alcohol drinking, diabetes, low frequency of laughter, psychological distress, and lower education levels in male subjects. In female subjects, baseline characteristics showed that a lack of sexual interest was associated with greater age, higher prevalence of abstinence from alcohol, low frequency of laughter, psychological distress, divorce or widowhood, and lower education levels. For both sexes, negative psychological variables, including psychological distress and low frequency of laughter, were associated with decreased sexual interest.

Interestingly, our study suggests that lack of sexual interest is associated with all-cause mortality in males, even after adjustment for age, diabetes, hypertension, dyslipidemia, smoking, alcohol intake, BMI, education, marital status, frequency of laughter, and psychological distress. Based on our results, we suggest that lack of sexual interest itself contributes to an increased risk of all-cause mortality, independent of established risk factors in men over 40 years old. However, it is possible that some important confounding factors were not identified or adjusted.

Although to our knowledge the mechanisms underlying the main gender difference result have yet to be clarified, men with ‘ikigai’ were at lower risk of cardiovascular mortality than men without ‘ikigai,’ subsequent to age and multivariate adjustment. Uzuki et al. found that lack of social support was associated with risk of all-cause mortality and cardiovascular mortality, and these associations were stronger in males than females [22]. Previous studies have shown that risk-reduction effects of positive psychological factors on all-cause mortality and incidence of stroke differed according to gender [11, 17, 18]. Ikeda et al. reported that in Japan men who were divorced or widowed were at higher risk of mortality than married men, whereas no similar trend was observed in women [23]. Based on these results, we speculate that maintaining sexual interest may be related to positive psychological well-being and ‘ikigai’ especially among men.

Precisely how a lack of sexual interest impacts on health and longevity remains unknown, although several possibilities can be considered. Male lack of interest may be related with unhealthy lifestyles. In this study, men who reported a lack of sexual interest included more current smokers and cases of diabetes. Furthermore, if we assume that sexual interest is related to positive psychological factors, the absence of interest may affect a range of inflammatory, neuroendocrine, and immune responses. Positive affect is related with reduced neuroendocrine, inflammatory, and cardiovascular activities [24]. Chronic psychological stress has shown an association with suppressed immune response and increased susceptibility to malignancy and infection [25]. Further study is required to clarify the mechanisms which underlie the preventive effects of sexual interest on mortality.

The strengths of this study are its prospective design and substantial sample size. In addition, adjustment was done using a number of well-known risk factors, including age, diabetes, hypertension, dyslipidemia, smoking status, alcohol intake, psychological distress, and medical history of depression. However, several limitations of the study should be noted. First, although we conducted multivariate analyses with adjustment for various potential confounding factors, some unidentified confounding factors may have remained. Moreover, we did not adjust for other medically relevant elements known to affect sexual function and longevity, such as neurological conditions, depression, and medications, because such information was not obtained in the baseline survey. Also, only a small number of depressed patients were included in this study. Second, we did not consider how the social regulation of sexuality differs among cultures. Similar research should be extended to other countries. Third, our question about lack of sexual interest focused on interest in the opposite sex; we did not control for sexual orientation.　Sasayama et al. reported that the prevalence of homoromantic attraction was 1.0% for females and 1.5% for males [26]. Based on these figures, the potential number of individuals in the present study with sexual interest in the same sex was estimated to be approximately 200 people. We therefore consider it unlikely that this number would have influenced our overall results. We suggest that future research should include lesbian, gay, bisexual, transgender, and questioning (LGBTQs) adults. Fourth, this study collected data on subjects who were at least 40 years old. Future research might also look more closely at the onset of decreasing interest in sex; for example, whether these results concern only men who had recently lost interest, or whether they extend to men who had little interest even when they were much younger. Fifth, all subjects participated in community-based annual health checks, and so they might have been more health-conscious and more socially active than the general population. In other words, some degree of selection bias might characterize our study sample.

Notwithstanding these limitations, the findings of this study support that idea that maintaining sexual interest has positive effects on longevity, especially in males. The Canadian government, through public health promotion materials, has begun to endorse sexual activity as one element of an “aging well” agenda [27]. In Japan, there is more prejudice about sex among the elderly than in the Western world. We hope our findings will help promote public health through advocating sexuality in Japan.