Men’s Testosterone Decline & Blood Sugar

With age comes wisdom, but it may also bring lower energy levels, shifts in body composition, and a metabolism that isn't quite what it used to be. For many men, these changes are a common experience often chalked up to "getting older," but they could be signs of testosterone decline and a more nuanced shift in hormone and metabolic health. 

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Testosterone plays a broad role in men's health, and levels naturally vary throughout life and between individuals, influenced both by age and lifestyle. This article examines the relationship between men's testosterone levels and glucose metabolism, and how each may affect health and well-being. 

What is Testosterone and How Do Levels Change in Men? 

Testosterone is a hormone that plays an important role in reproduction and sexual function, but it also heavily influences muscle mass, fat distribution, bone density, red blood cell production, and heart health. Both men and women have testosterone, but it's produced in much higher amounts in males, functioning as an anabolic steroid in the body. 

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Testosterone levels increase through puberty, with adult male total testosterone levels ranging from 300 to 1,000 ng/dL.¹ After age 35, testosterone levels start to decline gradually, but for some, this decline happens too rapidly.²  An estimated 30 percent of men between 40 and 79 experience low testosterone levels, which increases the risk of a range of health issues like sexual dysfunction, bone loss, diabetes, and hypertension.¹

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Aside from the natural age-related changes throughout puberty and in older age, testosterone levels in men are heavily influenced by several lifestyle factors. Diet, activity, stress, and sleep can all influence testosterone levels. Because many causes of low testosterone are related to lifestyle, it's possible to improve low testosterone by addressing these issues. 

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Improving your sleep, ensuring you're getting enough calories and micronutrients, including zinc, vitamin D, and magnesium, keeping your weight in a healthy range, and managing your stress levels can all support healthy testosterone levels and, in turn, metabolic health throughout life.³

Why Declining Testosterone Matters for Metabolic Health

Testosterone gets a lot of attention for its role in sexual function and reproductive health, but its influences on metabolic health are just as significant. Testosterone levels can affect body composition, energy expenditure, and how your tissues respond to insulin, making it an important player in men's health. 

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Declining testosterone levels may be accompanied by changes such as low energy, decreased muscle definition, increased abdominal fat, or greater difficulty maintaining or building muscle mass, even when exercise or diet hasn't changed. If you're wearing a continuous glucose monitor (CGM), you may notice differences in your glucose levels, including higher baseline levels, steeper spikes, and increased hunger or cravings.  Routine laboratory tests may also reveal higher fasting glucose levels, triglycerides, or HbA1c, all early warning signs of metabolic dysfunction. 

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While having type 2 diabetes increases the risk of low testosterone, the opposite is also true. Researchers looked at studies involving over 16,700 men and found that men with higher total testosterone had a 35 percent lower risk of developing diabetes than those with lower levels.⁴

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Understanding how testosterone and your metabolic health are connected can help you better support both as you age. 

The Relationship Between Testosterone, Blood Sugar Regulation, and Insulin Sensitivity

Testosterone and blood sugar regulation influence each other through multiple pathways, forming a complex, interrelated relationship. 

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At a cellular level, testosterone can increase the number of insulin receptors on cell surfaces, improving how well your cells respond to insulin and take glucose from the bloodstream for energy.⁵ Adequate testosterone helps keep your cells' insulin sensitivity high, while low testosterone increases the risk of insulin resistance. 

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Beyond the surface of the cells, testosterone also influences glucose transporters, particularly GLUT4, which are the proteins that actually shuttle glucose into your muscle and fat cells. Studies show that testosterone increases both the expression and activity of GLUT4, meaning your cells have more transporters available and those transporters work more efficiently.⁶ 

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Testosterone also affects a cellular energy sensor called AMP-activated protein kinase (AMPK), particularly in skeletal muscle. AMPK helps cells take up glucose even without insulin, providing a method of glucose metabolism that's independent of insulin. Research shows that testosterone increases AMPK expression and activity, providing another mechanism by which it supports glucose metabolism.⁷

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The anti-inflammatory effects of testosterone also contribute. Testosterone suppresses the inflammatory molecules produced by visceral fat tissue that interfere with insulin signaling.⁸ At the same time, testosterone can increase adiponectin, an anti-inflammatory hormone that enhances insulin sensitivity. 

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This relationship also works in the opposite direction. In the presence of insulin resistance, increased inflammation, and elevated leptin levels, the hypothalamic-pituitary-gonadal (HPG) axis, which controls testosterone production, is suppressed, lowering testosterone levels.^9,10

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This relationship creates a problematic cycle where low testosterone contributes to insulin resistance, which creates an environment that suppresses testosterone production, continuing in a loop. Body composition changes only exacerbate the problem, as low testosterone promotes fat gain and muscle loss, which increases insulin resistance, which in turn suppresses testosterone.

Testosterone and Its Relationship with Muscle Mass and Glucose Metabolism 

The effects of testosterone on body composition can be significant, as it influences fat deposits and muscle mass. 

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As an anabolic steroid hormone, testosterone plays a significant role in muscle mass and strength, with testosterone therapy regularly resulting in gains of 4 to 8 pounds of muscle mass and improvements in muscle function.¹¹ While maintaining muscle strength and mass is important for functional reasons, it's equally important for metabolic health and glucose metabolism. Because muscle is metabolically active, it helps remove up to 80 percent of glucose from the bloodstream after a meal.¹²

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Not only can low testosterone cause a decline in muscle mass, but it can also lead to increased visceral and abdominal subcutaneous fat. Not only is visceral fat tissue less metabolically active, but it also secretes pro-inflammatory cytokines, thereby increasing systemic inflammation and the risk of insulin resistance.¹³ 

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Through studying testosterone levels of those undergoing bariatric surgery, where visceral and abdominal fat quickly decline, researchers have discovered that low testosterone and visceral fat are bidirectionally connected: Low testosterone increases abdominal fat, while excess abdominal fat can also decrease testosterone.¹¹

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A 2024 study found that not only do testosterone and visceral fat exhibit an inverse bidirectional relationship, but low testosterone and insulin resistance also do so. A combination of the suppression of insulin's effects on the hypothalamic-pituitary-gonadal (HPG) axis, inflammation, and high leptin levels, a hormone produced by fat cells, is likely to blame for both declining testosterone and decreased insulin sensitivity.^9,10

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The relationship among insulin sensitivity, body composition, inflammation, and testosterone helps explain why testosterone levels are a marker of metabolic health. Understanding these connections can provide context for the glucose-regulation patterns that men may experience with age and lifestyle changes. 

How Men Can Use Glucose Data to Understand Metabolism

Understanding how your body processes glucose can help you make strategic changes to your diet and lifestyle to improve insulin sensitivity and metabolic health, which directly affects testosterone and other hormone levels. 

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Instead of a single snapshot from a fingerstick test or an average from an HbA1c, a CGM provides insight into continuous patterns showing how quickly your glucose rises after eating, how high it peaks, how long it stays elevated, and how much it varies hour to hour.

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While advice on what to eat, how to portion food, when and how much to move is a good place to start, a CGM can give you insights into how your body responds to that advice, providing you with hard data to use as you adjust your habits and see the results. 

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You can see how meal timing affects your patterns, whether eating protein before carbs reduces your spikes, how different types of exercise and the timing of that exercise impact your glucose, and how sleep quality and stress show up in your data. You'll also get insights into your glucose variability, which is how much your levels fluctuate throughout the day, which can be an early predictor of heart disease or diabetes down the road.¹⁴

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A CGM can help you better understand your metabolic health and provide information to share with your healthcare provider, enabling informed adjustments to your lifestyle and habits as you work toward your health goals. 

FAQs

1. What causes testosterone to decline in men?

Testosterone naturally peaks in late adolescence and gradually declines with age, driven by changes in hormone signaling between the brain and testes. Beyond age, body composition, physical activity, sleep quality, stress, nutrition, and overall metabolic health all influence testosterone levels. 

2. How is testosterone related to blood sugar? 

The relationship between testosterone and blood sugar is bidirectional. Low testosterone can contribute to impaired glucose regulation, whereas insulin resistance and metabolic dysfunction can suppress testosterone production through inflammation and disruption of hormone signaling pathways.

3. Can low testosterone affect insulin? 

Research consistently shows that men with insulin resistance are at a higher risk of low testosterone and that low testosterone can reduce insulin sensitivity. 

4. Does declining testosterone increase blood sugar? 

Declining testosterone doesn't directly cause blood glucose to rise, but it reduces insulin sensitivity and affects other mechanisms that regulate blood glucose, often resulting in elevated glucose levels. 

The Bottom Line

Testosterone and metabolic health have a complex and bidirectional relationship. Testosterone naturally declines with age; however, when levels are too low, the risk of insulin resistance and impaired glucose regulation increases. At the same time, excess visceral fat, inflammation, and insulin resistance can suppress testosterone levels, impacting multiple areas of men's health. Understanding how your body processes glucose and making adjustments to your diet and lifestyle to support your metabolic health can, in turn, support healthy testosterone levels. 

Learn More With Signos' Expert Advice

Healthy testosterone levels start with a healthy metabolism. Signos can help you better understand how what you eat, how you move, and other lifestyle choices affect your metabolic health, while providing expert insights into improving your glucose regulation by tracking patterns and implementing strategic adjustments.