Potatoes presented a paradox, because they have both high levels of potassium, a mineral associated with lower blood pressure, and a high glycemic index (meaning that after a person eats them, his or her blood sugar levels rise rapidly), which has been linked to increased blood pressure, the authors wrote in their study.
The researchers, based at Brigham and Women's Hospital and Harvard Medical School, followed over 187,000 American men and women for more than 20 years. Participants returned a questionnaire with updates on their health every two years, and another about their eating habits, including potato consumption, every four years.
"We found that participants who consumed four or more than four servings a week of baked, boiled or mashed potatoes, had an 11 per cent higher risk of developing hypertension," says lead author Dr. Lea Borgi. That's compared with participants who consumed one or less than one serving a month. But Borgi and her team noticed a higher risk only in women, and not in men.
She told CBC News that result was quite unexpected. "We would expect it to be the same for men and women." The author points out that the study does have limitations. Participants self-reported a diagnosis of hypertension, and questionnaires tend to be an imperfect way of tracking trends over a long period of time. And as potatoes are often eaten with salt and butter, increased sodium could explain hypertension.
There is one spot of relief for the spud-lovers of the world, with an accompanying editorial in the same BMJ edition, by Professor Mark Harris from the University of New South Wales in Sydney and Dr Rachel Laws from Deakin University in Melbourne.
Dr Laws, a research fellow from Deakin's Institute for Physical Activity and Nutrition, said it would be far more useful to look at a person's overall diet, rather than just one food. Dr Laws said findings from the study were far from clear cut.
"For example, in women they found eating baked, boiled and mashed potato was linked to increased blood pressure, but not for men," she said.
"Interestingly, eating potato chips or crisps was not linked to an increase in high blood pressure; indeed it showed a lower risk for men.
"There might be other factors explaining the findings."
Dr Rebecca Reynolds, a nutritionist and lecturer from the School of Public Health and Community Medicine at UNSW, also sounded a cautionary note about the study.
"It is more important to look at the whole diet of a person rather than demonise the potato," she said.
"I do not think it is a good idea to tell people to avoid healthier ways of cooking potatoes.
"The benefits outweigh the negatives. They provide great nutrients and fibre.
"It is one of the staple foods in Australia, to be included as part of a healthy, well-balanced diet."
