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.