Exclusive: Exploring the Mystery of How NMN-Class Anti-Aging Supplements "Restore Sexual Vitality"

When talking about daily life, it’s hard to avoid the topic of intimate relationships; when discussing anti-aging, reproductive aging is equally unavoidable.

Last year, we covered Sinclair’s research, which turned the urban legend of "NMN boosting ovarian function and rejuvenating menopausal women" into a formal academic report.

But what about its effects on men?

To be honest, our assistant has received many positive feedbacks from male readers about "regaining sexual vitality"...

Among these readers are those who love life and advocate for science. They are curious about the mechanisms behind this phenomenon and hope we can provide a satisfying explanation.

Regrettably, there are currently no experimental studies specifically addressing this question (and unfortunately, we haven’t saved enough to build our own laboratory yet). We can only analyze it based on existing evidence and reasonable inferences:

The primary manifestation of male sexual arousal and maintenance is penile erection[1]. Like all life activities, penile erection is regulated by both the nervous system (mental stimulation) and humoral factors (hormones)[2].

During intimate interactions with a partner, sensory stimulation, mechanical stimulation, and hormonal fluctuations work together. The parasympathetic nervous system instructs endothelial cells of the penile arteries to secrete nitric oxide (a vasodilator). This causes the corpus cavernosum to fill with blood; the swollen corpus cavernosum then compresses veins, trapping blood inside to maintain an erection[3].

Psychological factors play a significant role in inducing and maintaining erections. Negative emotions such as excessive excitement, tension, anxiety, depression, shock, or fear can easily lead to "failure"[4].

Therefore, the best way to distinguish whether "erectile difficulty" stems from psychological or physical factors is to observe nocturnal erections ("morning wood")[5]:
During the REM (rapid eye movement) sleep phase, the locus coeruleus (the sympathetic nerve center) cannot be activated, losing its inhibitory effect on penile erections. Erections occurring at this time are entirely controlled by involuntary physiological processes[6].

Physiologically healthy men (except those with severe depression and physical disorders) experience 3–4 involuntary erections per night[7].

On one hand, most vascular diseases—such as cardiovascular disease and diabetes—can cause erectile dysfunction (ED)[8]. NMN can help improve these conditions by increasing NAD+ levels[9], allowing some patients to regain a satisfying sex life.

On the other hand, in healthy men, the most important physiological factor affecting penile erection is testosterone levels[10].

Testosterone is crucial for maintaining nitric oxide synthase levels in the penis; testosterone deficiency directly triggers sexual dysfunction[11]. As age increases, testosterone levels decline, which is closely associated with a higher incidence of ED[12].

Dehydroepiandrosterone (DHEA) is a precursor for synthesizing testosterone and estrone, and is also linked to various anti-aging benefits[13].

The famous "rhesus monkey experiment" in anti-aging research confirmed that calorie restriction (CR) can increase DHEA levels[14]; NMN shares many overlapping mechanisms with CR[15], suggesting it may also boost DHEA. However, no current studies confirm that NAD+ supplementation directly increases DHEA levels.

Testosterone is biosynthesized from cholesterol, a process requiring multiple dehydrogenases and lyases—all of which use NAD+ or NADPH (derived from NAD+[16]) as coenzymes[17,18].

Even for the same enzyme, there are multiple isoforms that perform different functions and are distributed in different organs/tissues[19]. This explains why NAD+ supplementation can promote "testosterone enhancement" in men and "ovarian maintenance" in women—two distinct effects.

While most readers report improved sexual vitality, a small number have 反馈 ed the opposite: "I used to function well, but after taking NMN, I struggle."

After ruling out psychological factors, vascular diseases, and drowsiness (a common side effect in the first few weeks of NMN use due to circadian rhythm adjustments), if "erectile difficulty" persists, pay attention to the following factors:

Regular exercise can increase DHEA levels in both men and women[20], promoting a more youthful state; resistance training targeting large muscle groups is especially effective at boosting testosterone[21], enhancing male erectile duration and firmness.

However, more testosterone is not always better—"Excess leads to decline." Testosterone must bind to a limited number of androgen receptors (AR) to exert its physiological effects; free testosterone that cannot bind to receptors is converted into estradiol by aromatase[22]. Estradiol has a significant negative impact on male sexual activity[10].

If you are a well-trained bodybuilder, the combined testosterone increase from resistance exercise and NAD+ supplementation (via NMN) may exceed the capacity of your androgen receptors.

Taking fitness supplements adds complexity:
Studies confirm that in middle-aged and elderly men, additional protein intake (e.g., protein powder) after resistance training can counteract the testosterone-boosting effect of the exercise[24].

Injecting exogenous testosterone to aid fitness is far more problematic: Improper exogenous testosterone supplementation can easily cause feminization (e.g., gynecomastia), negatively feedback to the pituitary gland, reduce endogenous testosterone production, and in severe cases, lead to infertility[25].

Current academic consensus holds that testosterone has "different effects on internal desire vs. external function" in men: Exogenous testosterone enhances libido but fails to improve physical (organic) function[10]. This leaves users with "desire outpacing physical capability"—a real-life example of "the contradiction between people’s longing for a better life and insufficient material conditions."

If you take fitness supplements, consider pausing them to observe improvements.

Fat cells synthesize large amounts of aromatase, which promotes the conversion of NMN-boosted testosterone into estradiol. Losing weight can increase testosterone levels and improve sexual function[26].

Besides NAD+, nutrients like vitamin A, vitamin D, and zinc[27–29] are also crucial for testosterone synthesis. Zinc even inhibits aromatase[30]; deficiency in any of these nutrients can become a "bottleneck" for testosterone levels, causing low libido and sexual dysfunction.

You can supplement these nutrients while taking NMN; if your condition improves, it indicates you may have had a deficiency.

Hormonal regulation is an extremely complex biological process. Beyond the above factors, it is also affected by genetic heterogeneity, environmental factors (e.g., plasticizers), special physical conditions, and even gut microbiota[31].

If you have ruled out the above factors but still experience persistent "erectile difficulty" after taking NMN, we recommend undergoing a blood sex hormone test to further analyze the specific cause.

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