A lack of sexual interest may indicate an increased risk of an early death among men living in Japan, according to a newly published study.

The exact relationship between mortality and libido is something researchers will need to tease apart, though the researchers speculate a reduced sex drive could be a more visible sign of subtle underlying health issues.

The data came from 20,969 people (8,558 men and 12,411 women) aged 40 or older who had annual health checkups over a six-year span in Yamagata Prefecture, a mountainous region of Japan famous for its hot springs, temples, and natural beauty.

A team of researchers from Yamagata University looked at the subjects' levels of sexual interest as self-reported in an initial questionnaire, and in a follow-up survey conducted years later. Of the original 20,969 subjects, 503 had passed away in that time.

The researchers found cancer mortality and all-cause mortality were significantly higher for men who reported a lack of sexual interest.

That association held even when they controlled for factors including age, hypertension, diabetes, smoking, alcohol consumption, BMI, education, marital status, frequency of laughter, and psychological distress.

"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," the researchers write.

"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."

The study found women were more likely to report a lack of sexual interest than men were – 16 percent of female participants in their sample did so, compared with 8 percent of male volunteers – but it did not find a significant association between lower libido and mortality in women as it had in men.

Being a purely observational study, there's no way to conclude which – if either factor – is the cause and which is the effect.

It's possible lack of sexual interest among men could be linked to "unhealthy lifestyles," the scientists suggest.

"Furthermore, if we assume that sexual interest is related to positive psychological factors," they write, "the absence of interest may affect a range of inflammatory, neuroendocrine, and immune responses."

More research will be needed to understand what exactly is happening, but merely unveiling a potential connection like this is an important step, the researchers add.

There are also some important caveats to note in the study. A person's lack of sexual interest was determined from a single question on the initial baseline questionnaire: "Currently, do you have any interest in people of the opposite sex?"

Even if everyone understands what that question is asking, it excludes those attracted to someone of the same sex, as the researchers acknowledge.

"Any person who answered 'no' was defined as lacking sexual interest. Accordingly, sexual interest in someone of the same sex would be considered as 'lacking sexual interest' in this study," they write.

The researchers estimate their sample may have included roughly 200 LGBTQ participants, and due to the narrow question used in this study, there is thus reason to doubt at least some of that data. The study's authors call for future research to take this into account.

The new study also did not adjust for certain "medically relevant elements known to affect sexual function and longevity," the authors write, such as neurological conditions or medications the subjects were taking, since that wasn't part of the baseline survey.

Nonetheless, maintaining sexual interest just might yield positive effects on longevity. Despite the study's limitations, the researchers argue in favor of raising awareness of sexual interest as a factor in public health among older populations in Japan.

"The Canadian government, through public health promotion materials, has begun to endorse sexual activity as one element of an 'aging well' agenda. In Japan, there is more prejudice about sex among the elderly than in the Western world," the study's authors write.

"We hope our findings will help promote public health through advocating sexuality in Japan."

The study was published in the journal PLOS One.