Eating potatoes four times a week increases the brisk of high blood pressure, a study said.

Even eating mashed, boiled or baked potatoes is linked to an increased danger, because they are nearly as likely to raise blood pressure as eating chips, Health news reported.

Chips contain far more fat because of the frying process, which raises other health risks. But the researchers, from Harvard Medical School, think eating any form of potato too often can cause blood pressure problems.

Because potatoes have a high glycaemic index, these starchy carbohydrates rapidly transform into sugars in the body, triggering a sharp rise in blood sugar levels.

Over time, this may cause blood sugar problems, the researchers said.

The experts analysed data from 187,000 men and women tracked in three large US projects for 20 years. The results suggest women who eat regularly eat potatoes may be at slightly higher risk of suffering high blood pressure than men.

Overall, however, they found men or women who ate four or more servings a week of baked, boiled, or mashed potatoes had an 11 percent increased risk of high blood pressure compared to those who ate potatoes less than once a month.

Those who ate chips four or more times a week had a 17 percent higher risk of high blood pressure.

Replacing one serving a day of potatoes with one serving of non-starchy vegetables led to a 7 percent drop in the risk of high blood pressure, they found.

But eating crisps had no effect, the experts found.

The team, which also included experts at Brigham and Women's Hospital in Boston, Massachusetts, suggested the high glycaemic index of potatoes could be to blame.

High-GI foods release energy more quickly and therefore raise blood sugar more quickly.

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