Sunday, August 2, 2009

Blood Glucose, Cancer, and Coronary Heart Disease

Elevated blood glucose is most often associated with the symptoms of diabetes, such as retinal damage, kidney failure and peripheral neuropathy. However, the consequences of hyperglycemia are not confined to diabetics. As blood glucose values rise in nondiabetics, it is possible for them to experience an increased relative risk of cancer and of coronary heart disease as well.

In 2007, Par Stattin and colleagues published a prospective study that investigated a possible relationship between hyperglycemia and the risk of various forms of cancer. More than sixty thousand Swedish men and women with no previous history of diabetes were studied over a 13-year period. During that time approximately 2,500 cases of cancer were identified in the study group. The investigators looked at the relationship between fasting glucose levels and the risk of cancer in this nondiabetic population. Among the participants who had elevated fasting blood glucose, there were small but statistically significant increases in the relative risk for several specific types of cancer. These included pancreatic cancer, cancer of the urinary tract and malignant melanoma. In women there was an increased risk of endometrial cancer. Among women less than 49 years of age, there was an increased risk of breast cancer. On the other hand, in men there was actually a decrease in the risk of prostatic cancer as fasting blood glucose levels rose.

Nondiabetics were also shown to have an association between glycemic control and the risk of coronary heart disease in a 2005 study published in the Archives of Internal Medicine. In a prospective study, investigators followed 1321 nondiabetic adults to assess a possible relationship between the level of hemoglobin A1c (HbA1c) and the incidence of coronary heart disease.

Hemoglobin A1c measures the percentage of glycated hemoglobin in a patient's red blood cells. The HbA1c value provides a picture of a person's average blood glucose control for the previous 2 to 3 months. The normal range for HbA1c in people without diabetes is
4% to 6%. For diabetics, the American Diabetes Association recommends that the HbA1c be maintained at 7.0% or less.

The nondiabetic patients in the coronary heart disease study were followed for 8 to 10 years. In order to remove possibly confounding variables, when the data was analyzed, it was adjusted for age, race, sex, BMI, blood pressure, LDL cholesterol, HDL cholesterol, triglycerides and smoking status. The adjustments for these risk factors allowed the investigators to examine whether hyperglycemia might provide an independent risk factor for coronary heart disease. They found that when HbA1c was below 4.6%, the adjusted data showed no apparent relationship between glycemic control and an increased risk of coronary heart disease. However, as the HbA1c rose above 4.6%, the adjusted data showed that not only did the risk of coronary heart disease rise, but it did so at an ever-increasing rate. The study found that the risk of coronary heart disease in nondiabetics rose 2.4-fold with every 1% increase in HbA1c above 4.6%.

Findings similar to those seen in both of these studies have also been reported by other investigators, and references can be found within each paper. However, it is important to remember that correlation does not equal causation. The relationship between increased blood glucose in nondiabetics and the incidence of cancer or the incidence of coronary heart disease may rest upon variables that are not as yet defined. However, it is worth noting that it may be important even for nondiabetics to keep an eye on their fasting blood glucose and their HbA1c.


anne h said...

Stargazey - I don't always comment, but I always read. Well, I guess I am commenting now, eh?
Love your work.

Stargazey said...

Thanks, Anne H! Sometimes all the facts and figures are a bit much to slog through, so I appreciate both the commenters and the lurkers!

Nancy said...

very iteresting! I'm trying to avoid diabetes which took my mothers and grandmothers lives too young (55 and 62)and my best friend (41)...I appreciate your blog because I have so many people in my life who think I am fast forwarding myself to bad health by going low carb. This blog helps me explain it all to them.

Stargazey said...

Best wishes on your low-carbing adventure, Nancy! As you've found, one of the things that helps is knowing that the science lines up behind low-carb, not behind low-fat/low-protein/high-carb as the healthiest way to live. I'm glad to have you here!

Kazazi said...

Stargazey, I discovered you blog a few weeks ago and think it's an excellent resource for somebody keen to explore the science around lowcard diets etc.

Today, I came across a very interesting study that has me puzzled a little:

Fancy discussing this further either here or in a separate post?

Stargazey said...

Thanks for the comment, Kazazi.

The study you refer to, Low-carb diets linked to atherosclerosis and impaired blood vessel growth was done in mice. After 12 weeks of a diet of 12 percent carbohydrate, 43 percent fat and 45 percent protein they developed significant vascular disease.

When it comes to diet, it is not necessarily wise to compare mice and humans. While both are omnivores, humans spent much of their history hunting and eating animals. They ate some plant matter, but relatively litle of it. Mice will eat insects and dead things, but most of their diet consists of plant-based food. In order to be successful, each species would have developed its physiology to maximize its potential survival based on the food it normally ate. In other words, in terms of diet, a mouse is not a human.

The other thing is that we actually know what a low-carb diet does to the plaque in human arteries. Dr. William Davis is a cardiologist who writes the Heart Scan Blog to encourage his readers to measure, track, and reduce coronary atherosclerotic plaque.

He does this by instructing his readers (and his patients) to eliminate wheat, cornstarch and sugars from their diets. He has a few additional guidelines which you can read about here. At any rate, these people are following a version of a low-carb diet. In case after case, they are able to see a significant reduction in their coronary atherosclerosis with his program. And this is without the use of statins in most cases.

I don't know enough mouse physiology to know why they develop vascular disease on a low-carb diet. However, if you're concerned that low-carbing is ruining your arteries, get your doctor to set you up for a baseline CT heart scan (not a CT coronary angiogram--a completely different test) and then track your plaque score as you continue doing low-carb.

Stargazey said...

Kazasi, since I wrote the comment above, I have read a post on Hyperlipid and found out that these mice were genetically modified to be ApoE-/-. That is, they are completely lacking a gene that is necessary for fat metabolism. The press release Low-carb diets linked to atherosclerosis and impaired blood vessel growth mentioned that these were ApoE mice, but did not explain the implications of that for the study. The original abstract does specify that these were ApoE-/- mice, but the press release did not provide a link to the abstract.

At any rate, ApoE-/- mice completely lack a protein that allows chylomicrons and VLDL to be taken up by the liver. As a result, cholesterol-rich particles will accumulate in the blood of these genetically-modified mice. On mouse chow, which is 15% fat, the mice have five times the normal serum plasma cholesterol and develop spontaneous atherosclerotic lesions. Increase their fat intake to 43% and they get very sick in just 12 weeks.

In humans, the ApoE-/- condition is apparently either very rare or nonexistent. You may draw your own conclusions as to the applicability of this study for guidance in your decision whether or not to use a low-carb diet.