Sex is a natural, common, and pleasurable part of human life, yet its impact on the health of the brain is surprisingly understudied.

A longitudinal study on life, sexuality, and mental sharpness in the US has now shown that sexual activity in older people, who do not live in nursing homes, is linked to better cognitive function down the road.

The dataset is nationally representative and includes information on how often Americans have voluntary, partnered sex (not necessarily intercourse), the level of pleasure they derive from that sex (orgasm or no), and how emotionally satisfying they find their sexual relationships.

The cognitive function of participants was determined via an official scoring process, which considers aspects of attention, memory, language, conceptual thinking, calculations, and orientation.

When analyzing the study data, sociologists Shannon Shena from Hope College and Hui Liub from Purdue University found that sex is linked to better brain health across all age groups considered, albeit in subtly different ways.

Among those aged 75 to 90, the frequency of sex appeared to be key. This group was found to have significantly better cognitive function five years on if they were currently having sex at least once a week.

For adults aged 62 to 74, on the other hand, the most important factor for future brain health was the quality of sex being had, in terms of both physical and emotional aspects.

"As seen in our sample, promoting sexual quality among younger-old couples may be a way to combat the interruptions which people anticipate to come with aging," Shena and Luib suggest, "and these feelings of sexual quality may manifest in their later cognitive health."

Partnered sex, after all, is not just an activity for the young. Studies show it continues in over half of people aged 62 and over.

But while research has found that sex can have mental and physical health benefits, including improved cardiovascular health, reduced distress, and improved happiness and well-being, its impact on the health of the aging brain is largely unknown.

Numerous studies have noticed that loneliness and social isolation are associated with cognitive decline in later life; however, these analyses do not often consider one of the most intimate types of social activity: sex.

What's more, some experts think that a lack of social activity is a repercussion of cognitive decline and not a cause of it.

Nevertheless, the models that Shena and Liub ran in their study suggest that the link between sex and cognitive health does not go both ways.

In other words, they found better cognition was not predictive of sexual activity five years on.

"It was surprising that there were no significant results in how cognitive functioning was related to sexual activity or sexual quality five years later," explains Shena to Eric W. Dolan at PsyPost.

"While it may seem that cognitive functioning may be related to sexuality, we're really not seeing evidence for that, even when we focused on different age and gender groups. Instead, the results point to the importance of sexuality and how it contributes to later health outcomes."

The findings suggest at least some types of social activity really might have a protective role against cognitive decline, though more research is needed among larger cohorts and over longer periods of time.

Interestingly, while older male cognitive health was linked to high physical pleasure in the current study, this connection was not observed in older female participants.

That said, no other differences between the sexes were observed. Race, ethnicity, education level, marital status, and self-rated physical and mental health also did not appear to be influencing factors.

Shena and Liub have put forward several explanations for their results.

First, sex often involves physical exercise, which means improved cognitive performance may be due to improved cardiovascular health, which, in turn, can increase blood flow to the brain and reduce inflammation.

Sex is also known to reduce stress, and stress is thought to prevent the neuronal growth in some parts of the brain associated with memory.

Lastly, sex may improve cognitive function through the release of dopamine, which is a neurotransmitter linked to improved memory.

"Our findings help to contextualize a multifaceted understanding of healthy aging and speak to clinical practices and policy decisions regarding cognitive health," write Shena and Luib, "and in particular how it may be related to sexual life, an often overlooked area for older adults."

The study was published in The Journal of Sex Research.