Are Potatoes Linked to High Blood Pressure?

Whether you like your potatoes boiled, baked, mashed or as chips, new US research has linked them to an increased risk of developing high blood pressure.

However, other experts argue that no direct cause-and-effect has yet been proven and studying dietary patterns is more useful than concentrating on individual foods.

A Look at Potato-Eating Habits

Researchers based at Brigham and Women's Hospital and Harvard Medical School decided to look at whether higher long-term intake of potatoes could be associated with an increased risk of high blood pressure (hypertension). To their knowledge, no one has previously examined a link between potatoes and high blood pressure. Their study is published in The BMJ.

The researchers combined the results of three large US studies that followed over 187,000 men and women for more than 20 years. A questionnaire was used to look at people's diets intake, including how often the participants ate potatoes and in which form. They included baked, boiled and mashed potatoes as one category, as well as potato chips and potato crisps as two separate categories. Reports of high blood pressure were based on diagnoses made by healthcare professionals.

After considering other risk factors in their analysis, the researchers found:

· When compared with less than one serving a month, consuming four or more servings a week of baked, boiled or mashed potatoes could be linked to an increased risk of high blood pressure in women, but not in men.

· Higher consumption of potato chips could be linked to an increase risk of high blood pressure in both men and women.

· Potato crisps could not be linked to an increased risk of high blood pressure in either men or women.

Because potatoes have a high glycaemic index when compared to other vegetables, the researchers have suggested that the raised blood sugar following eating them might trigger mechanisms that are associated with hypertension, and also mention that a diet high in carbohydrates such as potatoes may result in obesity, another risk factor for raised blood pressure. They recommend replacing a serving a day of boiled, baked or mashed potatoes with a serving of a non-starch vegetable - such as peas, butter beans, sweetcorn or sweet potatoes - to decrease the risk of high blood pressure.

A Call to Look at More Than One Ingredient

While acknowledging the important role diet has in the prevention and early management of high blood pressure, an editorial also published in The BMJ argues that dietary behaviour and patterns of eating are complex and difficult to measure.

Professor Mark Harris from the University of New South Wales in Sydney, and Dr Rachel Laws from Deakin University in Melbourne, warn that "there is a broader problem with exploring associations between risk of disease and intake of single nutrients or foods" that do not consider overall dietary patterns. They note that questionnaires do not usually collect detailed information on cooking methods and that it is possible that uncontrolled factors could affect the researchers' observations and analysis. For example, a habit of eating French fries may indicate there is also a dietary pattern of higher salt and saturated fat that is not captured in the questionnaire and therefore not adequately considered in the analysis of the data.

They suggest that studies that examine the links between various dietary patterns and risk of disease "provide more useful insights for both policy makers and practitioners than does a focus on individual foods or nutrients." They point out that the numerous studies and recommendations about specific foods - some of which are conflicting - pose a major challenge for consumers as well as for clinicians giving advice on diet to lower the risk of disease.

We Love the Spud - But Is It a Veg or a Starch?

Because potatoes are easy to grow and are an inexpensive source of vitamin C, they were a staple in the British diet during the Second World War, replacing meat and dairy products that were scarce at the time - and potatoes are still an important part of the our diet. Potatoes are also high in potassium, which may help prevent hypertension. A 2015 potato consumer report found that, of meals eaten at home, fresh potatoes were included in about 5.8 billion meals each year and frozen potato products end up on plates in 2.8 billion meals.

Although potatoes are technically a vegetable, they are usually eaten as a starchy food, in much the same way as bread, pasta and rice, explaining why the Department of Health has recently added them to their list of wholegrains as a good source of fibre, especially when eaten with their skins. When cooked without salt or fat, potatoes are considered a healthy nutrient-dense food, providing us with a significant amount of fibre, potassium, vitamin C, vitamin B6 and folate - and they are low in calories.

In the USA, rather than counting potatoes as a starch, they have recently been included in the fruit and vegetables category - and one of the main reasons is because white potatoes have a high amount of potassium, which is linked to lower blood pressure.

SOURCES:

The BMJ: 'Potato intake and incidence of hypertension: results from three prospective US cohort studies

The BMJ editorial: 'Are there bad foods or just bad diets?'

British Nutrition Foundation: 'New nutritional insights for health professionals'

NHS Choices: '5 A DAY: what counts?'

AHDB Potatoes, a division of the Agriculture & Horticulture Development Board: 'Market Intelligence, In-home Consumption'