Do potatoes increase your risk of high blood pressure?
Potatoes could increase your risk of high blood pressure, reports have suggested, but is there any truth behind the headlines?
The media coverage is based on an American study, published in the BMJ, that aimed to find out if eating more potatoes is associated with an increased risk of high blood pressure.
The researchers, from Harvard Medical School, looked at more than 187,000 men and women in three large American studies. It compared people who had less than one serving a month of baked, mashed or boiled potatoes, chips, or crisps, and people who had four or more servings a week.
They found that there was an 11 per cent higher risk of high blood pressure (hypertension) if participants had four or more servings a week of baked, boiled or mashed potatoes, and 17 per cent higher risk for French fries (chips), compared to people who had less than one serving a month. They found no increased risk with a higher consumption of crisps. However, a portion of crisps in the study was much smaller by weight than the other forms of potato (28g/1oz of crisps compared with 4oz /113g of French fries), so it might be that the smaller amount of potatoes affected the results.
The study showed that swapping a portion of potatoes for a portion of vegetables could reduce the risk of high blood pressure.
We can’t conclude that potatoes cause high blood pressure
Potatoes were being looked at because, while they are a source of potassium which is linked to blood pressure lowering, they are also high in carbohydrates. The effect of the glycaemic load (the effect of a portion of the carbohydrate containing food on blood glucose concentration after eating) could potentially be associated with effects on the body that could influence the development of raised blood pressure.
The BHF view
Victoria Taylor, Senior Dietitian at the British Heart Foundation, said: “This type of study can only show an association, not cause and effect. So we can’t conclude that potatoes cause high blood pressure and we cannot explain the cause of the results seen in the study.
“It is also important to note this is a study from the US where dietary guidance and recommendations vary from the UK. For example, in the UK potatoes are not included in the 5-a-day recommendations for fruit and vegetable consumption. While potatoes are part of the starchy carbohydrates section of the Government’s Eatwell guide, we must remember that, as with all foods, it’s important to consider the overall balance of the foods we eat.
“Nearly 30 per cent of adults in the UK have high blood pressure so it is key that we understand the condition and its causes as much as possible. This is why the British Heart Foundation is currently funding millions of pounds worth of research projects across the UK into high blood pressure.”
Limitations of the research
Although the researchers adjusted for differences in risk factors between the people who ate more potatoes and those who ate less, it’s hard to be sure that there were not other things that affected the findings. Also, the finding that swapping a daily portion of potatoes for non-starchy vegetables could have been due to the health benefits of vegetables rather than the potatoes. We’re all recommended to eat at least 5 portions a day of fruit and vegetables, which doesn’t include potatoes (except sweet potatoes).
The diagnosis of hypertension was based on information from the participants rather than measurements taken during the study, so there could have been some room for error.
The amount of potatoes that people ate was also self-reported, and in one of the studies this questionnaire was filled out every four years. It could be difficult for people to accurately report how many servings of potatoes they ate three or four years ago.
The scientists did not measure people’s salt intake or overall dietary patterns, which could have had an effect on their blood pressure, for example the mashed potatoes could have been served with a lot of butter and salt, or a higher consumption of French fries might mean people eat more takeaway foods in general which tend to be high in salt.
The media coverage
The story was covered widely, including in the Daily Mail, Guardian, Independent, Telegraph and Evening Standard.
The Standard’s headline was “Eating too many potatoes ‘raises the risk of high blood pressure'”, however the link has only been established as an association, it’s not possible to say the relationship is cause and effect from this research.
The Guardian reported that Public Health England, which advises the government about its nutrition guidelines, would not be changing its advice as a result of this study.
The Mail reported that “Baked are as bad as chips - but crisps have no effect”. However the study analysed baked potatoes together with mashed and boiled potatoes, so we cannot single out baked potatoes to compare them with chips.
The Daily Telegraph also said that there was “no association between eating crisps and high blood pressure” but this is not necessarily true. The study focused on the effects of potatoes rather than salt, so adjusted for the effects of salt in the diet. We know that crisps are often high in salt, and over time, too much salt can lead to high blood pressure.