What is blood pressure? Blood circulating through the body moves with a certain force - that's your blood pressure. This force can be affected by how strongly the heart is pumping and by the size of the vessels the blood is moving through. Blood moves through large arteries into smaller vessels called arterioles, which can expand and contract. When they expand, blood pressure goes down. When they contract, blood pressure goes up.
How is blood pressure measured? The pressure is measured in millimeters of mercury (mm Hg) at two points - when the heart beats (systolic) and when the heart is between beats (diastolic). Usually blood pressure readings are stated with the systolic in front of (or over) the diastolic - for example, 110/75 mm Hg. Systolic and diastolic pressure are both important, but after you reach 50, systolic becomes more important because it gives a measure of how flexible your blood vessels are - or are not.
DASH, which stands for Dietary Approaches to Stop Hypertension, stems from an eight-week clinical trial that tested the effects of three different diets on 459 adults, 133 of whom had high blood pressure.
One diet was fairly similar to what many Americans eat; another had more fruits and vegetables and fewer snacks and treats.
The third - which came to be known as the DASH diet - was rich in fruits and vegetables but also included a lot of low-fat dairy products and whole grains, as well as less saturated fat, total fat and cholesterol.
Those in the DASH group reduced their blood pressure readings more than the two other groups.
The effectiveness of the DASH diet in reducing bad outcomes - as opposed to just blood pressure - isn't as clear. But a 2008 report suggested that it does lower the risk of heart disease and stroke, and two studies published last year found that it lowers the risk of heart failure.
Excess salt can lead to excess fluid retention in the blood. This makes the circulatory system fuller and the pressure inside it greater. Also, salt can make small blood vessels called arterioles contract, which shrinks the circulatory system, again increasing the pressure inside it.
A Jan. 21 study published in The New England Journal of Medicine concluded that if everyone in the United States consumed half a teaspoon less of salt every day, every year the number of new cases of coronary heart disease would drop 60,000; stroke, 32,000; and heart attack, 54,000 - and the number of deaths from any cause each year by 44,000.
But the relationship between salt and high blood pressure is complex.
In some salt-sensitive people, blood pressure responds dramatically to changes in salt intake. In others, not so much.
It's hard to tell who's salt sensitive and who isn't - there's no simple test. But many factors seem to matter, including family history, race/ethnicity (African-Americans are more likely than others to be salt sensitive), age, weight and diet.
Given the ambiguities, most medical experts say that limiting salt consumption is a good general rule. Between 1,500 and 2,300 mg of sodium a day are considered plenty for healthy adults - that's a teaspoon of salt or less - and if you're older than 50, or you're African-American, or you have other risk factors for salt sensitivity, you should stick to the low end of that range.
Potassium, fish oil, fiber
One relatively unsung hero in the battle against high blood pressure may be potassium. Results haven't been unanimous, but a good deal of research suggests that healthy doses of the mineral can be very good for your health - and that includes by cutting blood pressure.
One 2001 study, published in the Archives of Internal Medicine and based on data from more than 17,000 U.S. adults, found that people who ate 8.5 servings a day of fruits and vegetables (about 4,100 mg of potassium) had lower blood pressures than people who ate 3.5 servings (1,700 mg) - on average, 7.2 systolic units and 2.8 diastolic units lower.
Other studies have found a blood pressure-lowering link for both fiber and fish oil. A review of 25 trials published in 2005 found that dietary fiber was associated with average reductions of 5.95 systolic units and 4.2 diastolic units in trials lasting at least eight weeks.
Most studies about the effects of exercise on blood pressure have looked at aerobic exercise, although some evidence shows that resistance training may also be effective. Recommendations call for exercising every day (or at least most days) for 30 to 45 minutes. (Moderate exercise may be just as effective, and possibly more, than higher intensity exercise.) Blood pressure can drop in just a few weeks of regular exercise. It can also pop right back up if you stop exercising.
Just why exercise lowers blood pressure isn't clear, but there are several possible explanations:
•Exercise makes your heart stronger, so it doesn't have to pump as hard, which in turn lowers the force on your arteries.
•High blood insulin levels have been linked to high blood pressure - and exercise is known to reduce insulin levels.
•Regular exercise also reduces the level of adrenaline in the body, and that, in turn, lowers your heart rate and blood pressure.
Here's our standard, boilerplate reminder: It's always important to consult your doctor before beginning an exercise program - especially if you already have high blood pressure.
As people gain weight, their blood pressure tends to go up. Fortunately, as they lose weight, their blood pressure also goes down - but only so far, says Dr. Karol Watson, co-director of preventive cardiology and director of the hypertension clinic at UCLA.
"If your body weight is normal, getting below doesn't help," she says.
Even modest weight loss is effective at lowering blood pressure for those who already have high blood pressure and also for those in the high normal or prehypertensive range - that area where your readings are elevated but not high enough to be defined as clearly high.
The way you lose that weight may matter, however.
For some people, at least, losing weight by following a low-carbohydrate diet leads to a greater reduction in blood pressure than losing the same amount of weight by following a low-fat diet and taking the prescription-strength "fat-blocker" orlistat (Xenical, Alli), according to a Jan. 25 report in the Archives of Internal Medicine. Though the association between weight and blood pressure is well established, it isn't well understood. Many believe it's related to food. "If you're overweight, you're usually not eating the healthiest diet," says Dr. Mitra Nadim, director of the Hypertension Center at the University of Southern California.
But a 2002 study suggests that it may also be related to decreases in amounts of angiotensin-converting enzyme, or ACE, which plays an important role in blood pressure regulation.
Everyone agrees that stressful situations make your blood pressure take off. It's the fight-or-flight, prepare-to-do- something-dramatic response your ancient ancestors had when being charged by a woolly mammoth. You're likely to have it when, say, the Super Bowl is about to start and you can't find the remote.
Your body releases stress hormones that make your heart beat faster and your blood vessels constrict, with the result that your blood pressure rockets. When the stressful situation is resolved, though, your blood pressure comes back down.
Some scientists suspect that getting stressed out too often can lead to chronic high blood pressure. That's still not proven. But even if it doesn't, whenever your blood pressure is higher than it should be, it increases wear and tear on your blood vessels. So a plethora of stress, leading to a plethora of blood pressure spikes, can do the same sort of damage that high blood pressure itself can do.
Some - but not all - stress-reduction techniques have been shown to lower high blood pressure.
For example, a number of studies have found that reducing blood pressure may be as simple as breathing — slow, regular breathing. In one, researchers studied 66 patients with Type 2 diabetes and uncontrolled high blood pressure. All of the patients continued whatever treatment they were already on, and half of them also used a device that induced slow, regular breathing by playing musical tones that set a rhythm for the patients. They used the device 15 minutes a day for eight weeks.
Blood pressure went down for patients using the device, but it did not go down for the patients who didn't use the device.
Another study showed that people with high blood pressure could lower it by taking six slow breaths a minute. The slow breaths seemed to improve the body's ability to adjust blood pressure on a moment-by-moment basis.
Alcohol, smoking and caffeine
Is a bad habit ever a good thing? It can be - kind of - if your aim is to lower your blood pressure now. One way to lower your blood pressure is to reduce your alcohol consumption. It's a winning strategy - but only, of course, if you were drinking a lot in the first place.
Many studies have documented the link between alcohol and blood pressure. A 2001 review of 15 alcohol-reduction trials with 2,234 participants concluded that on average, cutting back on alcohol led to reductions in blood pressure. The greater the alcohol reduction, the greater the blood pressure reduction.
Some scientists believe that red wine, in moderate amounts, may improve vascular function and have a less harmful effect on blood pressure than other forms of alcohol - maybe even a positive effect. But this was not supported by a 2005 study that found drinking red wine and beer increased systolic blood pressure by about the same amount.
Any time you smoke a cigarette, it can produce an immediate - but temporary - surge in blood pressure because of the nicotine. But there's no evidence that smoking increases your chances of developing chronic high blood pressure. Still, smoking and high blood pressure appear to have a synergistic (greater than additive) effect on the risk of hemorrhagic stroke. So quit, already.
Like nicotine, caffeine can make your blood pressure shoot up temporarily, especially if you're not used to it. But, as with cigarettes, there's no definitive evidence that drinking a cup of coffee every day - or maybe a couple of cups - increases blood pressure over the long term. And some research suggests that if you do consume a lot of caffeine, you get used to it, and your blood pressure doesn't react so much anymore.