Morning wood, also known as nocturnal penile tumescence (NPT), is a phenomenon most men experience throughout their lives. During sleep, the body enters a parasympathetic state, releasing acetylcholine and nitric oxide (NO), which causes the dilation of blood vessels. Testosterone secretion follows a diurnal secretion pattern, peaking in the early morning, further promoting morning wood. When the body is in good health, men can expect around five episodes of tumescence over a single night (1). Although it may not be practical to track nighttime erections, whether or not you wake up with one is a crucial indicator of health. 

Nighttime erections have been the subject of scientific interest since the 1940s. Preliminary research focused on NPT's ability to delineate physical and mental etiologies of erectile dysfunction (ED). The theory is that a man who struggles to achieve and maintain an erection during intercourse but wakes up erect has ED originating primarily from mental distress. In contrast, the man with erectile difficulty in the bedroom who also finds himself flaccid in the morning likely suffers from underlying endothelial dysfunction and hormonal imbalance. One review of NPT's diagnostic utility concluded, "NPT reflects central neural and endocrine processes." Erectile quality acts as a window into systemic vascular function (2). 

"The term "endothelial dysfunction" refers to a maladapted endothelial phenotype characterized by reduced NO bioavailability, increased oxidative stress, elevated expression of pro-inflammatory and pro-thrombotic factors, and abnormal vasoreactivity." (3) 

Erection frequency and quality serve as valuable heuristics for health. ED is not solely a matter of sexual potency. Often it is the first warning sign of silent cardiovascular disease. One study reported three-quarters of men who had a heart attack began experiencing erectile dysfunction three to five years prior, bolstering the theory of a temporal relationship between them (4). Another study confirmed ED's predictive value, reporting it confers a 46% increased risk for cardiovascular disease (5). Vasculogenic ED most often stems from defective nitric oxide (NO) signaling. Inadequate NO concentrations leave endothelial walls constricted and more susceptible to plaque formation. Given their mutual pathogenesis, patients with ED should receive a comprehensive cardiac risk assessment. 

Insulin resistance (IR) precedes and exacerbates many diseases, including ED and CVD. Decreased insulin sensitivity results in blood sugar dysregulation, vascular damage, and impaired NO signaling. Unsurprisingly men with diabetes are three times more likely to face ED. A review of young men with ED believed to be of psychological origin found 52% of them to have underlying insulin insensitivity (6). IR is strongly implicated in hypogonadism, another cofactor for ED. TRT can significantly improve glycemic control in insulin-resistant men and help restore erectile function (7). While PDE5-inhibiting medications remain a safe and effective treatment for early onset ED, thorough metabolic screening can uncover whether impaired glucose metabolism is an underlying factor. 

The absence of morning wood with associated ED can also point toward hormone imbalances. Adequate levels of sex hormones are required for healthy erections. Testosterone promotes NO synthesis and supports the influx of calcium ions into endothelial cells, which allows for optimal circulation. Thyroid hormones play an integral role in arousal, and abnormal T3/T4 can contribute to premature and delayed ejaculation (8). Prolactin, a hormone responsible for female lactation, can worsen ED if it becomes elevated in men (9). Hyperprolactinemia typically stems from pituitary tumors but can also occur secondary to chronic antidepressant use. 

Mindfulness of morning wood can serve as a non-invasive means to assess for vasculogenic disease, hormonal imbalance, and metabolic dysfunction (10). Don't ignore this potential warning sign. If you've noticed fewer episodes of morning wood, are experiencing erectile dysfunction, or want to optimize your general and sexual health, you have come to the right place. 

Disclaimer: This blog post/article is for informational purposes only and does not constitute medical advice. This is not a substitute for professional medical advice and should not be relied upon. If you are considering a treatment, always consult your primary care physician to discuss the risks and benefits.

Citations and References: 

1. Nocturnal penile tumescence in the evaluation of erectile disorders

2. The role of nocturnal penile tumescence monitoring in the diagnosis of impotence

3. Role of insulin resistance in endothelial dysfunction.

4. The temporal relationship between erectile dysfunction and cardiovascular disease.

5. Current diagnosis and management of erectile dysfunction

6. Insulin resistance is an independent determinate of ED in young adult men.

7. Testosterone replacement therapy improves insulin resistance, glycaemic control, visceral adiposity and hypercholesterolaemia in hypogonadal men with type 2 diabetes.

8. Effect of Thyroid Hormone Derangements on Sexual Function in Men and Women 

9. Hyperprolactinemia and erectile dysfunction. 

10. Is the History of Erectile Dysfunction a Reliable Risk Factor for New Onset Acute Myocardial Infarction? A Systematic Review and Meta-Analysis.

11. One patient out of four with newly diagnosed erectile dysfunction is a young man--worrisome picture from the everyday clinical practice 

12. Erectile dysfunction prospectively associated with cardiovascular disease in the Dutch general population: results from the Krimpen Study

13. Erectile dysfunction, metabolic syndrome, and cardiovascular risks: facts and controversies

14. Reference ranges for testosterone in men generated using liquid chromatography tandem mass spectrometry in a community-based sample of healthy nonobese young men in the Framingham Heart Study and applied to three geographically distinct cohorts. J Clin Endocrinol Metab.