More Insight into What Blood Pressure Level is Safe

People with diabetes have been told for the past five years that they should shoot for a lower blood pressure target than the normal population, ideally one under 120/80. However, recent research is refining the usefulness of this recommendation.

Blood pressure control is the second most import step a person with diabetes can take. That is because high blood pressure promotes both heart attack and kidney failure. These are among the most dreaded complications of diabetes.

But, as I have learned the through my own experience, for some of us striving for the 120/80 blood sugar target can be a problem, because blood pressure tends to drop during the night. When my blood pressure is under the 120/80 target in the daytime I am prone to wake up at 4 AM with the pounding pulse and throbbing heart that occur when my blood pressure has dropped so low that a counterregulatory response kicks in to raise it. I also tend to develop postural hypotension when I am taking blood pressure drugs and may keel over and nearly black out when working in my garden if I kneel down and stand up too often.

So the latest news about how low blood pressure needs to be to maintain health is very reassuring.

The first piece of it is a Cochran Review look at blood pressure studies. The chief researcher here concluded, "'At present there is no evidence from randomized trials to support aiming for a blood pressure target lower than 140/90, in the general population of patients with elevated blood pressure.'"

You can read more about this in the Science Daily report: Blood Pressure Targets: Aiming Lower Produces No Benefit Review Finds.

As reported in Science Daily,

The review is based on the results of seven trials, which together involved 22,089 people. Whilst patients aiming for targets below 135/85 mmHg did succeed in achieving greater reductions in blood pressure than those in the standard target group, there was no difference between the two groups in terms of the number of patients dying or suffering heart attacks, strokes, heart failure or kidney failure.

The researchers noted that they did not break out the data for people with diabetes separately. The study also did not draw conclusions about whether it is safe to lower blood pressure aggressively.

Another study published in the American Journal of Kidney Diseases may provide a bit more insight into when borderline blood pressure becomes dangerous.

Prehypertension, Obesity, and Risk of Kidney Disease: 20-Year Follow-up of the HUNT I Study in Norway. John Munkhauge et al. American Journal of Kidney Diseases doi:10.1053/j.ajkd.2009.03.023 Article in press 8/11/2009.

This study is particularly compelling because it is a huge epidemiological study that studied the relationship of borderline blood pressure and kidney failure over a period of 20 years.

The subjects were 88.2 percent of all inhabitants 20 years or older in Nord-Trøndelag county, in mid-Norway. This kind of broad reach means that the study was more likely to include all kinds of people of all social and economic classes. The one major limitation is that being they were in Norway, the racial mix of the population would have been very limited compared to the population you'd find in a county in middle America.

This study's findings are informative for people with diabetes because, though they did not examine risk specifically relative to diabetes (the medical definition of which has changed greatly over the 20 year period of the study), they did look at risk relative to obesity.

What the Norway study found was this: Borderline blood pressure, defined as blood pressures between 120/80 and 139/89 were not associated with a higher risk of kidney failure or cardiovascular related death until BMI rose over 30.*

This BMI correlates to a weight of 175 lbs in a woman 5' 4" tall or of 203 lbs in a man 5' 9" tall. You can compute your own BMI HERE.

However, while risk rose in the borderline blood pressure category the study also found "In participants with BP less than 120/80 mm Hg, risk did not increase with increasing BMI." [emphasis mine]

BMI can be very deceptive because it doesn't distinguish between body fat and muscle mass, so an athlete may be classified as obese while having a normal or even low body weight percentage.

For example, when my son was playing college football he had a BMI of 32 which is well into the "obese" category, but his body fat was measured at 17%, which is far from obese. But if you aren't a teenaged boy who leg presses 700 lbs, the BMI is usually a pretty good guide to how fat you are.

This study points to two important conclusions.

If you are not obese as defined by BMI, you are probably fine maintaining a blood pressure lower than 139/89.

If you are obese, you should shoot for a blood pressure of 120/80.

This robust long term epidemiological data also appears to back up the NHANES finding that I've blogged about before that overweight is a healthy weight, especially for people in the latter half of life. Overweight is officially defined as having a BMI of 25-29.

If you are trying to lose weight this data might convince you that it is worth shooting for a weight that gives you a BMI under 30. For any of us is an attainable goal--and one we are far more likely to reach than the dream weights suitable for people in their early 20s most obese dieters shoot for.

Choosing an attainable realistic goal is one of the keys to successful dieting. This is because unrealistically low weight goals often derail people's diets. A goal set too low is a goal the dieter can't reach. That failure often frustrates otherwise successful dieters to the point where they often blow off their diet because they still think they are fat--even if they have lost 20, 30 or even 100 lbs.

If you can get to a BMI of 29 you have succeeded, as far as your health goes. For that matter, if you have lost any significant amount of weight you've done something positive for your health. Risk for many conditions rises along with weight as it continues to rise over that 30 BMI.

Set that 30 BMI weight as your first and most important goal. If you can do better. Great! If not, you can rest assured that you have done what you need to do to maintain your health.

One nice thing about blood pressure is that, unlike the case with blood sugar, you can buy a blood pressure meter for a one time charge and test your blood pressrue as often as you want without ever having to pay for a single consumable.

It is a good idea for any person with diabetes to invest in a blood pressure meter and get into the habit of checking your blood pressure now and then to make sure it isn't rising dangerously high without your realizing it. If you see blood pressures over 139/89 make an appointment to talk to your doctor about it. Doctors are much better at treating blood pressure than blood sugar.

I recommend a blood pressure meter that plugs into the wall not the slightly cheaper meters that run on batteries. Long term they are cheaper and you don't end up with unpredictable results from failing batteries. Use a meter that measures arm pressure, not wrist pressure. The arm meters are more accurate. I like the Omrons, personally. They are a lot cheaper on Amazon than at the drug store.

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* The mention of cardiovascular related deaths comes from the report of this study in Science Daily: Prehypertension, Obesity And Kidney Disease Risks