Insulin and Prostate Cancer: What’s the Link?

Medically Reviewed by Nazia Q Bandukwala, DO on May 27, 2024
6 min read

Prostate cancer is the most common type of cancer in men. More than 1 in 10 men will get it at some point in their life. Your chances of getting prostate cancer will depend on many different things: your age, family history, genetics, diet, weight, and more. Another thing that can influence your prostate cancer risk in complicated ways is your insulin level.

Your body needs the hormone insulin to control blood sugar (glucose). When you have diabetes or prediabetes, your body stops responding to insulin the way it should. Doctors call this insulin resistance. Your body will respond by making more insulin. Your blood sugar levels also will go up.

What’s this have to do with prostate cancer? The connections between insulin, blood sugar, diabetes, and prostate cancer might surprise you. They certainly seem to not make sense at first. Studies have linked higher levels of insulin to a greater risk of prostate cancer. Diabetes comes with an increased risk for many cancer types and plenty of other health problems. But it turns out that people with diabetes are actually less likely to get prostate cancer than those who don’t have it. At the same time, people with diabetes who get prostate cancer more often do worse.

One study of 100 people from Finland with prostate cancer and another 400 without it looked for links between the cancer and insulin or blood sugar levels. The researchers knew that insulin might play a role in prostate cancer. Insulin can make cells grow, but it wasn’t really clear how levels of insulin in the bloodstream could increase prostate cancer risk.

To try and understand it better, they looked at levels of insulin and blood sugar 5 to 10 years before the men got prostate cancer. Their data showed that insulin levels more than 9 years before prostate cancer were 8% higher in those who got the cancer compared to those who didn’t.

Their insulin levels still were in a range that was considered normal. So the men with higher insulin in this study didn’t have diabetes or another condition. But those with the highest insulin levels were more than twice as likely to get prostate cancer compared with those with the lowest insulin levels. They didn’t see the same pattern with blood sugar. Men with blood sugar levels on the higher end didn’t show more prostate cancer risk.

Higher levels of insulin tend to go along with insulin resistance. When your body doesn’t respond to insulin as well, it makes more. Another study of men in China found a similar link. Men who were the most sensitive to insulin as indicated by low levels of the hormone were less likely to get prostate cancer. Men who were more resistant to insulin and had higher levels of it (but not diabetes) got prostate cancer more often.

One study looked at 45 studies of prostate cancer and diabetes from 1970 to 2011. It found that men with diabetes have a 14% lower risk of prostate cancer compared with men who don’t have it. But if more insulin and insulin resistance make prostate cancer more likely, you might wonder how diabetes could lead to lower prostate cancer risk. One possible reason is that diabetes is linked to lower levels of testosterone. Testosterone has a connection to prostate cancer growth, so lower testosterone might protect against this cancer.

Researchers didn’t know much about men who were on the way to diabetes but didn’t have it yet. To find out, they looked at almost 6,000 men who later got diabetes compared with 28,000 who didn’t. They found that prediabetes didn’t offer any protection against prostate cancer. So diabetes is protective, but prediabetes isn’t. The study also suggested that diabetes offers more protection against prostate cancer the longer you have it.

How can this be? One way to understand this is that cancers, including prostate cancers, take up lots of sugar to feed their growth. But the amount of sugar they take up has more to do with available insulin than it does blood sugar. That’s because insulin turns on certain proteins that allow cancer cells to take in and use blood sugar.

The other thing to consider is that people with diabetes often take medicine to lower their blood sugar. For this reason, people who’ve had diabetes for a long time actually may have low insulin levels compared with someone without diabetes. This is because over time, the cells in the pancreas that make insulin begin to die off, so insulin levels go down and blood sugar goes up. Someone with diabetes usually needs more medication over time.

Studies have shown that people with diabetes who take the first-line medication (called metformin) are less likely to get some cancers, including prostate cancer. Metformin works to lower blood sugar. But it doesn’t increase insulin levels. So when people take metformin, both blood sugar and insulin tend to go down. Low insulin levels in people taking medicine for diabetes might help to explain why they’re at lower prostate cancer risk. But doctors still don’t know exactly how or why diabetes and diabetes medicines affect prostate cancer.

Even though people with diabetes get prostate cancer less often, it still happens. Both conditions are quite common, so it is not unlikely for an aging male to experience both. While diabetes seems to make prostate cancer less likely, people who have it and get prostate cancer are more likely to die from it. But keep in mind that most people don’t die from prostate cancer. The 5-year relative survival rate for prostate cancer is almost 97%. That’s because prostate cancers are usually slow growing and detected before they’ve spread to distant parts of the body.

Some studies suggest that prostate cancers in people with diabetes more often spread to lymph nodes. The prostate cancers in those with diabetes also tend to have certain features that make for worse outcomes. For instance, one study found that prostate cancers in people with diabetes responded more to hormones that make them grow.

Another study found that outcomes for those with diabetes and prostate cancer depend on how the diabetes is managed. Men who either took insulin for their diabetes or who didn’t take medicine for it at all more often did worse. So, if you have prostate cancer and diabetes, it’s a good idea to see your doctor and make sure you keep your diabetes under control.

The verdict is still out as to whether or not having diabetes raises your risk for prostate cancer. There seems to be a negative connection between insulin resistance and diabetes. We need more research to understand how insulin levels, diabetes, and prostate cancer are related.

It’s a good idea for anyone to take steps to keep their insulin levels low. That’s especially true if you have prostate cancer or any other cancer type, since insulin may fuel cancer’s growth. The best way to lower insulin levels whether or not you have diabetes is to exercise and eat a healthy diet. Keeping the weight off and exercising can help your body respond to insulin and prevent or delay diabetes. Taking metformin also can help. If you have prediabetes or your insulin levels are even on the higher end of the normal range, ask your doctor what they recommend.

If you or a loved one has diabetes and prostate cancer, ask your doctor what you can do to improve your chances of a good outcome. Rest assured most prostate cancers are caught before they spread and generally have positive outcomes. If you are worried you might have prostate cancer or may be at higher risk, talk to your doctor about whether you should think about tests to look for it.