A Link Between Diabetes And High Blood Pressure

Almost 75% of people with diabetes have high blood pressure (greater than or equal to 130/80 mm Hg).¹

Why?

We know that having consistently high blood sugars can damage arteries, predisposing them to plaque buildup and atherosclerosis. Those physical changes in the arteries can contribute to high blood pressure over time.

But a recent study in the journal Circulation Research² shone a light on a more specific mechanism.

Researchers found that blood pressure anomalies in diabetic rats were associated with an increase in the activity of an enzyme called arginase.

Here's the process by which increased arginase activity can lead to high blood pressure:

1. Arginase competes with another enzyme, nitric oxide synthase (NO synthase), for their common substrate - the amino acid arginine.
   
2. Arginase converts arginine to ornithine and urea. This is the last step of the liver's urea cycle, a process the body uses to rid itself of harmful ammonia. (Ammonia is produced in our bodies by the breakdown of nitrogen-containing compounds such as proteins.)
   
3. NO synthase converts arginine to nitric oxide (NO). NO mediates vasodilation - it lowers blood pressure.
   
4. When the pool of arginase is great, it can deplete available arginine, leaving little for NO synthase to act upon ... resulting in higher blood pressure.

The researchers also found that when bovine endothelial cells (cells that line blood vessels and heart cavities) were treated with high levels of glucose, it increased their arginase activity ... and lowered NO production. Less NO = less ability for blood vessels to relax.

L-arginine is marketed as a supplement to lower blood pressure. But if people with diabetes have increased arginase activity, that arginase could deplete both endogenous (inside the body) as well as exogenous (taken as a supplement) arginine before NO synthase has a chance to act upon it. A more promising supplement, garnered from these researchers' work, may be another amino acid, L-citrulline, which was shown to blunt the effect of arginase.

Furthering our understanding of how diabetes and high blood pressure are linked can help researchers discover or develop therapies to manage hypertension. However, one drug-free, inexpensive approach that's available right now is good management of blood glucose.
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¹ National Diabetes Information Clearinghouse, Diabetes Dateline, New Fact Sheet On High Blood Pressure And Kidney Disease

² Diabetes-Induced Coronary Vascular Dysfunction Involves Increased Arginase Activity

News summary (ScienceDaily):
Diabetes Makes It Hard For Blood Vessels To Relax

A Heart Attack Is A Hard Lesson

The New York Times posted an article this morning on the importance of treating various aspects of the metabolic syndrome that accompany diabetes, not just blood glucose:

Looking Past Blood Sugar to Survive With Diabetes

It chronicles the story of Dave Smith, a 43-year-old pastor from Fairmont, Minnesota. He was diagnosed with type 2 diabetes when he was 34. Since the time of his diagnosis, he dieted, watched his carbohydrate intake, lost weight, and took medications to lower his blood glucose. When that proved ineffective, he added insulin to the mix.

Eight years of failing to address conditions that often accompany diabetes (e.g. high blood cholesterol and high blood pressure) proved a hard lesson for Mr. Smith and his healthcare providers. He landed in the hospital with a major heart attack - 90% of a prime artery to his heart was blocked.

You can watch Mr. Smith describe his ordeal by clicking the photo below:


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A Chocolate Study Worth Its Cocoa

A small study that appeared in the Journal of the American Medical Association this month found that eating just 6.3 grams of dark chocolate a day can reduce blood pressure (BP).¹ Previous studies found a BP-lowering benefit with eating dark chocolate, but the amounts tested were often in the 100 gram range. This is the first study to document benefit with such a small amount.

Participants of the study were 44 adults with either upper-range prehypertension or stage 1 hypertension (see chart) . After 18 weeks, those who were consuming 6.3 grams (about 1 square inch) of dark chocolate daily reduced their systolic BP by an average of 2.9 mm Hg, their diastolic by 1.9 mm Hg. (This is about the reduction seen in participants of the HOPE Study who were on an ACE inhibitor.)



The chart is extracted from the NIH's brochure: The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure.

If you'd like to give this a try, you may want to eat the small amount of chocolate every day. In this study, there was no BP-lowering effect for the first 6 weeks. A gradually increasing effect became apparent after that, with the strongest effect at the end of the study (18 weeks).

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¹ Effects of Low Habitual Cocoa Intake on Blood Pressure and Bioactive Nitric Oxide

New Blood Pressure Guidelines Prove Challenging

A new study in the January issue of Diabetes Care found that the more aggressive guidelines for treatment of hypertension which were released in 2003:

"... did not result in substantially better hypertension control for patients with diabetes in the US."¹

Below are the most recent classifications for blood pressure as described in the JNC's 7th Report:²


Click Chart for Full Version.

And here are the JNC's summarized recommendations for lifestyle modifications. (More information about the blood pressure guidelines and lifestyle recommendations, including eating plans, can be found here.)


Click Chart for Larger.

________¹ Lack of Effect of Guideline Changes on Hypertension Control for Patients With Diabetes in the U.S., 1995–2005, Diabetes Care, January 2007.

² The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure, Express Report, published in 2003 by the National Heart, Lung, and Blood Institute (NHLB), a division of the National Institutes of Health (NIH).