Blood Pressure Control: As Important as Blood Sugar Control?

Several recently published studies remind us that high blood pressure plays an important role in causing several of the classic diabetic complications and that controlling high blood pressure may be nearly as important as controlling our blood sugar.

Blood sugar and blood pressure are not unrelated. In fact, there is some evidence that suggests that high blood sugars cause high blood pressure. Many people who have cut the carbohydrates out of their diet find that their blood pressure drops--sometimes dramatically--after making this change. Some people attribute this to the fact that for an insulin resistant person with Type 2 diabetes, cutting the carbs will lower the amount of insulin that is secreted, and suggest that insulin itself raises blood sugar. Others think it might be related to the diuretic effect of the low carb diet.

But it is more likely that high blood sugars themselves cause high blood pressure. That this might be the case is suggested by the findings of the 15 year follow-up to the DCCT study.

DCCT was the landmark study where people with Type 1 diabetes were given more aggressive treatment with the goal of lowering their A1cs to 7%. Before this study, most doctors did not believe that lowering blood sugar could prevent diabetic complications. The DCCT proved them to have been very wrong as blood sugar in these Type 1s lowered the incidence of their diabetic complications dramatically.

The EDIC study which was a follow up involving the DCCT subjects after the original study was over found that, "However, intensive therapy during the DCCT reduced the risk of incident hypertension by 24% ... . A higher hemoglobin A1c level, measured at baseline or throughout follow-up, was associated with increased risk for incident hypertension..."

Subjects involved in the DCCT study used more insulin, not less than controls with higher blood sugars, and they were eating a high carb/low fat diet so no diuretic effect would have been involved. Even so, the follow-up study found that the lower the A1c the better their blood pressure was.

Insulin Therapy, Hyperglycemia, and Hypertension in Type 1 Diabetes Mellitus Epidemiology of Diabetes Interventions and Complications. (EDIC) Study Research Group. Arch Intern Med. 2008;168(17):1867-1873.

The UKPDS, was an attempt to duplicate the DCCT study using a population of people in the UK diagnosed with Type 2 diabetes rather than the Type 1 that had been studied in DCCT. It found that lowering both blood sugar and blood pressure greatly decreased microvascular complications.

The follow up to the UKPDS study found a more sobering relationship between blood sugar and blood pressure.

Long-Term Follow-up after Tight Control of Blood Pressure in Type 2 Diabetes New England Journal of Medicine. Volume 359:1565-1576. October 9, 2008. Number 15.

Unlike the Type 1s studied in the DCCT follow up study, the Type 2s involved in the UKDPS follow up study did a wretched job of controlling their blood sugars. This wasn't their fault. The study design says it all. "The 884 patients who underwent post-trial monitoring were asked to attend annual UKPDS clinics for the first 5 years, but no attempt was made to maintain their previously assigned therapies."

In short, once the study was over, were offered only the standard UK NHS treatment which meant they were told to eat a high carb/low fat diet, given sulfs or metformin, and, if they were given insulin at all, they were given the extremely outdated one or two shots a day 70/30 NPH regimens that were standard NHS treatment until very recently.

They were not encouraged to lower their blood sugars to the feeble 7% A1c that the UKPDS researchers had striven for, and it is not even clear if they were ever informed that there were any health benefits to lowering their A1cs to the 7% level.

What happened to these people was sobering. Not surprisingly, their blood sugars soared. And so did their blood pressures. As reported by the researchers, "Significant relative risk reductions found during the trial for any diabetes-related end point, diabetes-related death, microvascular disease, and stroke in the group receiving tight, as compared with less tight, blood-pressure control were not sustained during the post-trial follow-up."

Saddest of all, the improvement in microvascular complications that had been seen during the "tight control" phase of the study ("tight control" here was defined as a 7% A1c) disappeared as blood pressure rose along with blood sugar.

The researchers conclude "Early improvement in blood-pressure control in patients with both type 2 diabetes and hypertension was associated with a reduced risk of complications, but it appears that good blood-pressure control must be continued if the benefits are to be maintained."

I will restrain myself from ranting and raving about the ethics of a study where patients who had achieved significant improvements via tighter blood sugar control were completely abandoned once the researchers had their data in the can. Instead, I wall point to the take away message here: Lowering blood sugar lowers blood pressure and decreases microvascular complications. If you let blood sugar go back up again, blood pressure will go up too and you see a lot more microvascular complications.

Microvascular complications include retinopathy and nephropathy--in English, blindness and kidney failure. The kidney is particularly sensitive to damage from high blood pressure, which appears to destroy its glomeruli--tiny filtration units.

A sub-study connected with UKPDS found a dramatic drop in retinopathy and stroke in a group of people with Type 2 who were given either an ACE inhibitor or a beta blocker to lower their blood pressure. Their target blood pressure was one that today's doctors still consider too high: 150/85, but even so, achieving that target produced a dramatic lowering of stroke and retinopathy.

Tight blood pressure control and risk of macrovascular and microvascular complications in type 2 diabetes: UKPDS 38. UK Prospective Diabetes Study Group.

So there are two lessons here:

1. Lowering blood sugar should help control blood pressure and that may be one reason why lower blood sugars help prevent diabetic complications.

2. Lowering blood pressure independent of blood sugar can also help prevent serious diabetic microvascular complications.

This should motivate you to keep an eye on your blood pressure as well as on your blood sugar. Just relying on the blood pressure measurement your doctor does every couple months--or perhaps once a year--is not enough to prevent high blood pressure from creeping up and causing microvascular damage.

Fortunately, blood pressure monitoring is a lot cheaper than monitoring blood sugar. For about $60 you can buy an automated blood pressure meter that you can use at home. The Omron meters sold on Amazon for $50 - $60 (Shipping is free) are highly accurate and well worth the investment.

When shopping for a blood pressure meter, avoid the wrist models--they tend not to be as accurate. Also, look for one that plugs into the wall with an AC adapter rather than one dependent on batteries.

Once you have your monitor, check your blood pressure every couple days, following the instructions that come with your meter. Expect your blood pressure to fluctuate from day to day and at different times of day. But if you see repeated blood pressures where the first measurement is over 140 or the second measurement is over 90 give your doctor a call and make an appointment to discuss treatment.

If you see repeated blood pressure measurements over 180/100 you should demand to see a doctor immediately. Sustained exposure to blood pressures that high can damage your organs.

Some people find that exercise helps them lower blood pressure. A subgroup of people--this depends on genetics--are very sensitive to salt and for this group, cutting salt out of the diet can lower blood pressure too. For people not in this group, salt has no impact on blood pressures. You will only know what group you fall into by cutting your sodium intake and seeing if it has an impact on your blood pressure.

Doctors do not really understand all the reasons people develop high blood pressure. Other forms of kidney disease may play a part. So do fluctuations in the levels of many different hormones--sex hormones and cortical hormones in particular. But whatever the cause, untreated high blood pressure is very dangerous and a major contributor to stroke, heart attack, heart failure, kidney failure, and blindness. Lowering it can help prevent all these unpleasant conditions.