The old saying ‘An apple a day keeps the doctor away’ is certainly true when it comes to high blood pressure and its complications. Research shows that regularly eating apples is linked with a lower risk of developing high blood pressure, and a lower risk of the complications associated with hypertension such as heart attack and stroke. Apples also appear to have protective effects against type 2 diabetes, respiratory diseases, dementia and even some cancers.
As a result of all these benefits, researchers have calculated that eating an apple a day can reduce the risk of death from any cause, at any age, by one-third, compared with not eating any apples. For protecting against stroke, people who eat the most apples have a 41% lower risk of thrombotic stroke compared with those who eat the least.
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Apples lower a high blood pressure
The results of studies involving over 186,000 people found that people who eat 4 or more apples (or pears) per week are 9% less likely to develop hypertension than those who eat less than one apple per month, after taking all other risk factors into account.
One of the underlying causes of high blood pressure is over activity of a gene that produces an enzyme, ACE. This enzyme is a powerful blood vessel constrictor, and as ACE levels rise, so does blood pressure.
Apple peel contains antioxidants called flavonoids that act as ACE inhibitors, and have blood-pressure lowering actions similar to those of ACE inhibitor drugs. Apple flavonoids are also highly antioxidant and have additional protective effects on blood vessel walls to improve their elasticity.
The apple flavonoid with the most powerful antihypertensive effects is called quercetin. Quercetin helps blood vessels become more reactive, so they can dilate when needed to reduce blood pressure. Quercetin also has a unique effect on the kidneys to reduce sodium reabsorption and fluid retention in a similar way to some diuretic drugs prescribed to treat hypertension.
Medical researchers assessed the effects of adding dietary flavonoids to antihypertensive treatments (either an ACE inhibitor, captopril, or an angiotensin II receptor blocker, telmisartan) in 79 people with hypertension. The flavonoids were obtained from dehydrated red apple (30g), dark chocolate (30g) and two green tea bags (4g) per day to provide a daily dose of 425 mg flavonoids (epicatechin equivalents). Those taking part were asked not to eat other dietary sources of flavonoids during the course of the study.
In those taking the ACE inhibitor, the addition of dietary flavonoids lowered their blood pressure by an additional 5/4 mmHg compared with the ACE inhibitor alone. For those taking the angiotensin receptor blocker, the addition of dietary flavonoids lowered their blood pressure by an additional 43mmHg compared with the medication alone.
A study involving quercetin supplements found that taking a dose of 150mg per day reduced systolic blood pressure (the upper figure) by an average of 3.7mmHg in people with high blood pressure.
Another study found that taking quercetin supplements at a higher dose, of 730mg per day for 28 days, lowered blood pressure by 7/5 mmHg compared with placebo, but only in people with existing hypertension. Quercetin supplements did not affect blood pressure control in those with a normal blood pressure.
Apples protect against heart disease
Researchers have also found associations between flavonoid intake from apples and a reduced risk of death from all medical causes, especially from heart attack. After taking other risk factors such as age, smoking, cholesterol and weight into account, women with the highest intake of flavonoids from apples had a 43% less likely to experience a fatal heart attack compared to those with the lowest intakes, while for men the risk was reduced by 19%.
The best apples to lower blood pressure
Ripe apples vary in colour from bright red to yellow-orange and bright green. Red apples tend to provide higher levels of antioxidants than those that are green. A typical red apple provides over 200 mg polyphenols per 100g weight, including catechins similar to those found in green tea.
A type of apple called Renetta Canada, which has a golden peel with a red blush, was found to have the highest flavonoid levels of all. This variety is said to have a ‘sophisticated’ flavour while the peel develops a distinctive grainy texture when optimally ripe. Renetta is popular for cooking and is said to make great strudels and fritters. Red Delicious has the next highest polyphenol content of those tested, followed in order by Granny Smith, Morgenduft, Golden Delicious, Royal Gala, Braeburn and Fuji apples.
Flavonoids are found in all parts of an apple, but are particularly concentrated within the apple skin, whose levels are five to six times higher than those found in the juicy flesh. So before eating your apples, by all means wash them, but don’t even think about peeling them.
Clear apple juice has low levels of flavonoids, but cloudy apple juice is relatively rich as they aren’t strained out during the clarification process.
Apples lower cholesterol
Eating apples also helps to lower cholesterol levels, which are often raised when you have high blood pressure (as part of metabolic syndrome). When 160 women ate an apple a day for a year, their ‘bad’ LDL-cholesterol fell by almost a quarter. This is thought to result from the high level of soluble fibre found in apples, such as pectins, that bind cholesterol and bile salts in the gut so less is reabsorbed.
Apples improve glucose control
Apples contain fruit sugars, such as fructose and glucose, but even sweet dessert apples have a relatively low glycaemic index. The soluble fibre in apples, such as pectin, slows sugar absorption and helps to stabilise blood glucose levels. Apple flavonoids also protect insulin-producing cells in the pancreas from progressive damage and help to protect against poor glucose tolerance.
Eating apples may therefore protect against type 2 diabetes. One study involving over 187,000 people found that, for every three apples eaten per week, the risk of developing type 2 diabetes was reduced by 5%.
Another study, involving 38,000 women, those eating at least one apple a day were 28% less likely to develop type 2 diabetes than those who rarely ate apples.
Apples and weight loss
Eating an apple a day to lower your blood pressure won’t make you put on weight – in fact, it might even help you to lose weight. Researchers analysed the diet and lifestyle of over 133,000 men and women, and how any changes in their fruit and vegetable consumption affected their weight over a 4 year period. After adjusting for other lifestyle factors, such as exercise, they found that simply eating more apples was associated with an average weight loss of 1.11lb over a 4-year period, even if no other changes were made. And when 160 women added an apple a day to their diet, for one year, they lost around 1.5kg in weight – even though the apples provided additional calories.
How to add apples to your diet
Eat at least one red apple a day as a snack. Grate an apple, mix with lemon juice to prevent browning, and add to salads and coleslaw. Dried apple rings make a tasty snack. Apple crisps are available in health food shops, too.
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