Testosterone and Blood Sugar: The Insulin Sensitivity Link

By Dr. Farhan Abdullah, DO | Medical Director, Magnolia Functional Wellness | Southlake, TX

A man in his mid-fifties sits down across from me with two lab reports. One came from his primary care doctor and says his A1c is 6.1, which puts him squarely in the prediabetes range. The other is a testosterone panel he ordered on his own after a buddy at work started TRT, and it came back at 290 ng/dL. He slides both across the desk and asks the question I hear more than almost any other in November: "Are these two things related, or do I just have bad luck twice?"

They're related. Pretty tightly, in fact. I'm Dr. Farhan Abdullah, an internal medicine physician who still works hospital shifts in Dallas, and I'm the Medical Director at Magnolia Functional Wellness in Southlake. On the hospital side I see where uncontrolled blood sugar ends up: the foot wounds, the kidney numbers, the heart attacks in men who felt fine six months earlier. In the clinic I see the other end of the story, the men whose glucose and testosterone are both drifting the wrong way but nothing has broken yet. That second group is where we can still change the ending.

November is American Diabetes Month, so it's a good time to lay out what the research says about testosterone and insulin sensitivity. Some of it is encouraging. Some of it should cool off anyone who thinks a testosterone shot is a diabetes cure. Both halves matter.

Low testosterone and high blood sugar tend to show up together

The association is old news in endocrinology, but most men have never heard it. A 2006 systematic review and meta-analysis in JAMA by Ding and colleagues pooled 43 studies covering more than 6,400 men. In cross-sectional studies, men with type 2 diabetes had testosterone levels about 77 ng/dL lower than men without it. Looking forward in time, men with higher testosterone (roughly 450 to 600 ng/dL) had a 42% lower risk of going on to develop diabetes.

That's a big gap. It's also observational, which means it can't tell us which way the arrow points. My read is that the arrow probably points both ways.

Visceral fat, the deep belly fat that wraps around your organs, is metabolically noisy tissue. It converts testosterone into estrogen through an enzyme called aromatase, it drives low-grade inflammation, and high insulin levels suppress the liver's production of SHBG, the protein that carries testosterone in the blood. Put that together and you get a man whose total and free testosterone both slide as his waistline grows. So insulin resistance can push testosterone down.

Going the other direction, testosterone helps you build and keep skeletal muscle, and muscle is the single biggest place your body parks glucose after a meal. Less testosterone usually means less muscle, more fat, and fewer places for sugar to go. So low testosterone can push insulin resistance up. Each problem feeds the other. I tell patients it's less of a chicken-and-egg question and more of a vicious circle, and the useful question is where we can break it.

What testosterone does inside the cell

Why would a sex hormone have anything to do with how your body handles a plate of enchiladas? Part of the answer lives in your mitochondria.

A 2005 study in Diabetes Care by Pitteloud and colleagues took 60 men, average age about 60, and measured their insulin sensitivity with a hyperinsulinemic-euglycemic clamp. That's the gold-standard test, the one researchers use when they want a real answer instead of an estimate. They also measured VO2 max and looked at gene expression inside muscle biopsies. The results were striking. Testosterone levels tracked with insulin sensitivity, with aerobic capacity, and with the activity of the genes that run mitochondrial energy production. The men with hypogonadal testosterone levels had about three times the rate of metabolic syndrome as the men with normal levels.

One caveat the authors were upfront about: once they adjusted for BMI, the metabolic syndrome link weakened. That tells you body fat is doing a lot of the work here. Testosterone and body composition are so tangled together that it's hard to pull them apart cleanly in a study of 60 people.

Still, the picture makes physiologic sense. Muscle with well-functioning mitochondria burns glucose and fat efficiently. Muscle with sluggish mitochondria lets fat build up inside the cell, and that intracellular fat interferes with insulin signaling. If testosterone helps keep that machinery running, then losing it would quietly erode your glucose handling long before your A1c tells on you.

The big trials: one said yes, one said not so fast

Association and mechanism are nice. What patients want to know is simpler. If I raise my testosterone, will my blood sugar improve? Two large randomized trials have tried to answer that, and they didn't land in the same place.

T4DM: testosterone plus lifestyle

The T4DM trial, published in 2021 in The Lancet Diabetes and Endocrinology by Wittert and colleagues, enrolled 1,007 Australian men aged 50 to 74. They all had big waistlines, testosterone at or below roughly 400 ng/dL, and either impaired glucose tolerance or newly diagnosed type 2 diabetes. Every man was enrolled in a community lifestyle program. Half also got injections of testosterone undecanoate every three months for two years. The other half got placebo injections.

At two years, 21% of the placebo group met the glucose threshold for type 2 diabetes, compared with 12% of the testosterone group. That's about a 40% relative reduction, and it held up regardless of where a man's testosterone started. Two-hour glucose on the tolerance test also dropped more in the testosterone group.

Now the part that doesn't make the headlines. Hematocrit, the concentration of red blood cells, climbed above 54% in 22% of the men on testosterone versus 1% on placebo. Thick blood is a real safety concern, and it's one of the main things we watch on every TRT patient. Serious adverse events were also somewhat more common in the testosterone arm.

TRAVERSE: testosterone alone

Then in 2024, a substudy of the TRAVERSE trial came out in JAMA Internal Medicine, led by Bhasin and colleagues. This one looked at more than 5,000 American men aged 45 to 80 who had confirmed hypogonadism plus either prediabetes or diabetes. They used a daily testosterone gel or a placebo gel, with no structured lifestyle program attached.

The result was flat. Progression from prediabetes to diabetes didn't differ significantly between the two groups, and men who already had diabetes didn't see better A1c or more remissions on testosterone. The authors concluded that TRT alone shouldn't be used to prevent or treat diabetes.

So which one is right?

Probably both, for different men under different conditions. T4DM paired testosterone with a real lifestyle program, used injections that produce steadier levels, and focused on men whose glucose was just starting to fail. TRAVERSE used a gel, which can be inconsistent in how much actually gets absorbed, and didn't build in diet and exercise support.

The way I read them together: testosterone isn't a diabetes drug. In a man who's truly deficient and who's also doing the work on food, training, and sleep, it may make that work pay off better. In a man who expects the hormone to do the work for him, the evidence doesn't back that up.

How we approach this at Magnolia

When a man comes in with low testosterone and a creeping A1c, I'm not interested in treating a number. I want the whole metabolic picture first. That usually means:

• Total and free testosterone, drawn in the morning and confirmed on a second draw, plus SHBG and estradiol
• Fasting glucose, fasting insulin, and A1c, so we can see insulin resistance before it becomes diabetes
• A lipid panel, liver enzymes, and a CBC with a baseline hematocrit
• PSA when it's age-appropriate
• Waist circumference and a body composition estimate, because the scale alone can mislead you
• A real conversation about sleep, since untreated sleep apnea lowers testosterone and worsens insulin resistance at the same time

Sometimes the answer is that testosterone therapy makes sense. If you want to see how we structure that, our testosterone replacement therapy program page walks through it. Other times the testosterone is low because the metabolic problem is driving it, and the better first move is to fix the metabolism and recheck in three months. I've had plenty of men drop 20 pounds, start lifting three days a week, get their sleep apnea treated, and watch their testosterone climb 100 points or more without a single injection.

When we do start TRT in a man with prediabetes or diabetes, the monitoring gets tighter, not looser. Hematocrit gets checked more often, because T4DM made it very clear how often it rises. We track A1c and fasting insulin alongside testosterone so we can tell whether the treatment is actually helping his metabolism or just helping his energy. Both are worth something, but they aren't the same thing.

What you can do this month, with or without TRT

Thanksgiving is two weeks away, and in Texas that means a holiday season of brisket, pecan pie, and football Sundays on the couch. I'm not going to tell you to skip all of it. I will tell you that the habits that improve insulin sensitivity are the same ones that protect your testosterone, so you get two wins from one set of changes.

Lift something heavy two or three times a week. Muscle is your glucose sink, and resistance training is the most reliable way I know to build it after 40. Take a 10 to 15 minute walk after your biggest meal, which blunts the post-meal glucose rise more than most people expect. Get seven hours of sleep, and if your partner says you snore like a leaf blower, get tested for sleep apnea. Go easy on the alcohol, since it hits the liver, the hormones, and your sleep all at once. And if your belly is growing while the rest of you isn't, take that seriously. It's the clearest outward sign of the visceral fat that drives this whole cycle.

Finally, if you have prediabetes or type 2 diabetes and you've never had your testosterone checked, ask for it. Low testosterone is common in men with diabetes, and it often goes unmeasured. The reverse is true too. If you've been told your testosterone is low, make sure someone has looked at your A1c and fasting insulin. If you're still sorting out whether TRT is even on the table for you, our guide on what men over 30 need to know before starting testosterone is a good place to begin.

The bottom line on testosterone and blood sugar

Low testosterone and insulin resistance travel together, and each one makes the other worse. The mechanism runs through muscle, belly fat, SHBG, and the energy machinery inside your cells. The best trial evidence says testosterone therapy can help some deficient men keep prediabetes from turning into diabetes, but mostly when it's paired with real lifestyle change, and it carries risks like a rising hematocrit that need close watching. It isn't a shortcut.

For the man with the two lab reports, we didn't start anything that day. We rechecked his testosterone, added fasting insulin, ordered a sleep study, and built a training plan he could stick to. Three months later we'll know a lot more, and so will he. If you're in Southlake, Keller, Grapevine, or anywhere else in the area and your numbers look like his, that's exactly the kind of workup we do at Magnolia Functional Wellness.