As research hits the news, since I speak and write about this on a regular basis, people often contact me with questions ranging from the scientific and metabolic to those about practical implications. Today in Smart Bytes®, fresh from seeing colleagues at the American Diabetes Association Scientific Sessions, I’ll answer a few of those common questions on the diabetes-cancer connection.
What is the connection of type 2 diabetes to cancer risk?
Type 2 diabetes is linked to several of the major cancer threats Americans face – colon, pancreatic and postmenopausal breast cancers, as well as cancers of the liver, kidney, bladder and endometrium, as well as non-Hodgkin lymphoma and perhaps other cancers. People with pre-existing diabetes also face a higher mortality rate if diagnosed with cancer. In some studies, the diabetes-cancer link appears weaker in men than in women. That’s because prostate cancer is one of the most common cancers in U.S. men, and most studies link diabetes to a lower risk of prostate cancer, probably due to hormonal changes that tend to accompany type 2 diabetes. Aside from prostate cancer, men’s risk of cancer increases with type 2 diabetes, also.
Some scientists questioned whether having type 2 diabetes actually changes cancer risk, or whether the two diseases occur together because they are both linked to several similar risk factors, including obesity, sedentary lifestyles, and smoking. Now we see that in studies adjusting for body mass index (BMI) as a marker of obesity or overweight, the connection of diabetes and cancer risk remains. Since other studies link metabolic abnormalities of diabetes like elevated insulin levels and inflammation to increased cancer risk, most researchers now say that these and other metabolic abnormalities of type 2 diabetes seem to directly increase cancer risk.
That’s exactly why we need to talk about this: The message isn’t about being doomed; it’s about knowing risks and taking actions that make a difference. Everyone needs to know, for example, that less than 10 percent of cancer risk comes from a specific inherited trait. More research is needed to get a clearer picture, but much of our cancer risk comes down to everyday choices in diet, tobacco, and physical activity, and how these choices add up to impact weight.
In a large European population study, for example, among people who followed recommendations from the American Institute for Cancer Research (AICR) most closely, cancer risk was 18 percent lower than among those who followed no more than three of the recommendations. Each one-point increase in score was tied to a five percent lower risk of cancer overall, with some types of cancer more closely linked to these lifestyle choices than other types. Many of these choices intersect with the link between diabetes and cancer.
What’s the overlap between healthy eating choices for type 2 diabetes and for reducing cancer risk?
People with diabetes often focus on adding up the grams of carbohydrate they eat in order to control blood sugar. Blood sugar control is important, but that alone is not enough to decrease chronic inflammation that seems to be part of the diabetes-cancer connection.
The same total carbohydrate can comes from a variety of food choices. For lower cancer risk (and better overall health), choose mostly plant foods that have not been processed in ways that remove healthful compounds or add excess fat, sugar or salt. Choosing foods that are good sources of dietary fiber is recommended to help control blood sugar levels in people with type 2 diabetes and prediabetes. Dietary fiber also shows a strong link to lower risk of colorectal cancer, and research suggests it may play a role in reducing risk of breast cancer, too.
Looking at total fiber content doesn’t tell the full story. Evidence like that shared at the recent American Diabetes Association conference I just attended shows that equal amounts of even the same type of dietary fiber can have different effects depending on the food in which it is found and your overall eating choices. We know that whole grains supply fiber, vitamins and minerals, and more than that. Whole grains provide natural compounds, such as polyphenols, that are antioxidants, and may also affect cell signaling pathways that influence cancer development. Phytochemicals in vegetables, fruits and dried beans are also antioxidants, and again may play an even more significant role in affecting cell signaling pathways and expression of genes (a field known as epigenetics).
Would cutting back on red meat help?
Excess red meat does increase risk of colorectal cancer. Analysis of nine separate population studies shows a 17 percent increased risk for each three-and-a-half ounces consumed daily. The reasons for this link may or may not involve the particular factors linking type 2 diabetes to cancer. However, since colorectal cancer risk is already increased, people with type 2 diabetes may want to look closely at AICR’s recommendation to limit red meat to no more than 18 ounces a week (and to avoid processed meats, which pose even greater risk).
Messages about diabetes emphasize choosing lean meats; to reduce cancer risk, limit the amount, too. Research is still in progress seeking to better understand red meat’s effects on cancer risk. Current work is looking at how heme iron (higher in red meat) may damage cells of the colon, as well as how red meat changes the bacteria that live in our colon, which could thus affect inflammation.
Does exercise make any difference if it doesn’t lead to weight loss?
Regular moderate exercise improves blood sugar control in type 2 diabetes and reduces risk of developing the disease. Physical activity’s healthful effects come from more than weight loss. The “insulin resistance” seen in type 2 diabetes (and the prediabetes that precedes it) means that the body cannot effectively use the insulin it produces. For 24 to 72 hours following a bout of moderate physical activity, changes in the body’s metabolic signaling decrease this insulin resistance. And not only does that lead to better blood sugar control, it means the cell signals promoting cell growth and reproduction change, too – which means less of a push for cells to develop into cancer.
The catch isn’t a requirement for weight loss; it’s frequency. Since these benefits last for only 24 to 72 hours, researchers suggest that getting some moderate exercise daily, or at least every two days, is the key to physical activity’s benefits. Aim to accumulate at least 30 minutes a day of moderate activity. If you are aiming for weight loss, studies show that for most people, with today’s sedentary lives, 60 minutes a day better supports weight loss. Regardless of total time goal, you still achieve beneficial effects if you break up activity in to 10- to 15-minute blocks. As you do this, focus on finding choices that are fun and de-stress or energize you, because the goal is to make this activity pattern a lifetime habit.
Bottom line message: Cancer ranks among Americans’ top health fears, so news of the link between type 2 diabetes and cancer risk may initially seem overwhelming. It’s tempting to look the other way and ignore the news. But research suggests that the choices you make about tobacco and also about food and drink choices and physical activity (including their impact on your weight), do make a difference. It’s also important to note that the link between diabetes and cancer involves metabolic changes seen in prediabetes. So don’t put off taking action. Do take steps to gain good blood sugar control, but don’t stop there. You can make choices that lower risk of cancer, too. Aim for overall health and vitality.
Let’s talk: What other questions do you have about the diabetes-cancer connection? Now – while it’s fresh on your mind — use the comments section below to let me know, and I’ll try to address them in a future Smart Bytes®.
If you aren’t familiar with steps everyone can take to reduce cancer risk, check this free American Institute for Cancer Research (AICR) brochure, 10 Ways to Reduce Your Cancer Risk.
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