Lifestyle change can affect blood pressure, but it's not the whole story

So how much good will it do if you get more exercise, consume less salt, ramp up on potassium, eat the DASH way, give up smoking, take up meditation? Does it all add up to some impressive total that will knock your doctor's socks off the next check-up time?

It depends a lot on where you start out. If you're a confirmed couch potato, exercising even a little might help to bring your blood pressure down. But if you're already a marathon runner, you've probably maxed out on the good that exercise can do you.

If you smoke two packs a day, quitting could make a big difference. If you're already a nonsmoker, that option doesn't even exist.

But it's also really tricky to add up the effect of all these individual actions because so many of them are interconnected.

For example, it's known that the nicotine in cigarettes increases blood pressure temporarily -- and yet some studies comparing populations of smokers with nonsmokers have found that smokers' blood pressure is actually lower on average. A possible explanation for this apparent paradox: Smoking helps people keep their weight down, so nonsmokers may have higher blood pressures on average because they're heavier on average.

Similarly, it can be hard to disentangle the effects of exercise and weight loss since one often leads to the other. And -- somewhat less obviously -- often the same people who don't get much sleep don't get much exercise either and are also likely to be overweight.

So, in studies of sleep and blood pressure, the blood pressure increases may be completely due to lack of sleep or partly due to a dearth of exercise and a plenitude of pounds.

Scientists try to take account of these confounding factors when they can, of course. And many studies have looked directly at the interactions of various factors.

For example, a study of 412 people published in the New England Journal of Medicine in 2001 found that a low-sodium DASH diet was even better than the plain DASH diet. Those on DASH (which stands for Dietary Approaches to Stop Hpertension) who dropped their sodium to an intermediate level (2,300 milligrams a day) skimmed an extra 1.3 mm Hg off their systolic blood pressure; those who dropped it still further to a low level (1,150 mg a day) dropped it by 1.7 mm Hg more. And that was on top of the 5.9 mm Hg benefits gained from a DASH diet alone.

In fact, the full potential of the DASH diet combined with low sodium is greater than drugs, says Dr. Frank Sacks, professor of cardiovascular disease prevention at the Harvard School of Public Health, lead author of that study.

Adding aerobic exercise and weight loss to the DASH diet also produces more of an effect than the DASH diet alone, according to a four-month study of 144 overweight or obese people with elevated blood pressure. People who were given weight loss counseling and followed an aerobic exercise program in addition to the DASH diet lost an average of about 19 pounds and knocked 16 points off their blood pressure, compared with just DASH (11 points) and a control group (3 points).

And a 2009 study of 3,000 participants found that the ratio of sodium to potassium was more important than either salt or potassium alone. Individuals with the highest sodium-to-potassium ratio in their urine were 50% more likely to develop cardiovascular disease in the next 10 to 15 years than those with the lowest ratios, the study found. The relationship wasn't found for high sodium or potassium levels when the ratio between the two wasn't taken into effect.

We all could stand to work on that sodium-potassium ratio. Instead of the 1-to-2 ratio recommended as the maximum by the Institute of Medicine, most Americans probably have a 1-to-1 ratio, or worse.

Sometimes the results of one study can shed new light on the results of others. For instance, in a 2009 study of sleep vis-a-vis blood pressure, researchers found that African American men slept much less than white women. This led them to suggest that sleep duration might be partly responsible for the well-known results that African Americans generally have higher blood pressure than other ethnicities, and men generally have higher blood pressure than women.