Blueberries May Ease Blood Pressure
Berries and other foods rich in antioxidants may also bring blood-sugar benefits
Berries and other foods rich in antioxidants may also bring blood-sugar benefits
Cardiovascular disease is the leading cause of death in the United States.
And once women go through menopause, this puts them at an even greater risk for it.
New findings suggest that blueberries may mitigate the negative cardiovascular effects of menopause.
Before we get into the details, some background is helpful to understanding why blueberries may benefit heart health.
A quick primer on polyphenols
Most plant foods abound in compounds commonly called “antioxidants”, which fall into two categories: carotenoids and polyphenols.
The various members of both groups are commonly called “antioxidants”, because they squelch the pro-oxidant compounds called free radicals … in test tubes.
However, carotenoids and polyphenols generally do not exert direct antioxidant effects in the body… at least not to a very substantial extent.
Instead, they exert indirect but highly beneficial effects via so-called “nutrigenomic” effects on gene switches (e.g., transcription factors) in our cells.
These nutrigenomic effects tend to moderate inflammation and stimulate the body's own antioxidant network … which includes enzymes, lipoic acid, CoQ10, melatonin, and vitamins C and E.
And there's ample evidence that foods rich in polyphenols deter the oxidative cell damage and inflammation caused by free radicals.
Top food sources of certain polyphenols – like grapes and blueberries – relax arteries in animals and people, and enhance artery-lining functions in ways that should support optimal cardiovascular health.
(The riches sources of polyphenols are berries, plums, prunes, red grapes, onions, cocoa (non-alkalized/Dutched only), dark chocolate, tea, extra virgin olive oil, beans, and whole grains.)
For example, see “Blueberries May Help Artery Health”, “Blueberries Aid and Relax Arteries”, and “Fish Oils and Blueberries Cut Cardio Risks”.
And a recent study from Harvard linked higher intakes of the major type of polyphenol in all berries – anthocyanins – to a reduced risk for heart attacks in 93,600 female nurses women aged 25 to 42 (Cassidy A et al. 2013).
Now, the results of an unprecedented clinical trial show that the polyphenols in blueberries can lower blood pressure … probably because of their artery-relaxing effects.
Blueberries drop women's blood pressure in clinical trial
The new trial comes from Florida State University's Center for Advancing Exercise and Nutrition Research on Aging (Johnson SA et al. 2015).
A team led by Sarah A. Johnson, Ph.D., conducted a randomized, double-blind, placebo-controlled trial involving 48 postmenopausal women aged 45 to 65 with pre- and stage-1 hypertension.
At the beginning of the study, the team took participants' blood pressure and measured their arterial stiffness and selected blood bio-markers for hypertension.
The women were randomly assigned to consume one of two things for eight weeks:
- 22 grams of a placebo powder
- 22 grams of freeze-dried blueberry powder (equivalent to one cup of fresh blueberries)
The participants continued their normal diet and exercise routines.
At the end of the eight weeks, the blueberry powder group enjoyed an average 7 mmHg (5.1 percent) drop in systolic blood pressure, which is the pressure generated in arteries by a heartbeat.
They also saw a 5 mmHg (6.3 percent) reduction in diastolic blood pressure, which is the pressure in arteries between heartbeats.
The participants in the blueberry- group also showed two other benefits:
- An average reduction of 97 cm/second (6.5 percent) in arterial stiffness.
- Nitric oxide, which widens blood vessels, increased by 68.5 percent.
According to Johnson, those two improvements help explain the drops in systolic and diastolic pressure, because arterial stiffness and the width of blood vessels influence blood pressure.
Previous studies on blueberries have shown positive effects on cardiovascular risk factors including blood pressure, but they all included large amounts of blueberry powder consumption, anywhere from 50 grams to 250 grams.
Those amounts of blueberry powder are equal to two cups and more than 11 cups of fresh blueberries, respectively … quantities no one could or would eat even once, much less on a regular basis.
Of course, these results don't mean that you need to eat a cup of blueberries daily … just that they tend to moderate blood pressure.
(We should note that the research was funded by the U.S. Highbush Blueberry Council.)
As Dr. Johnson told The New York Times, “There is something very special about the composition of blueberries that is responsible for their effect on blood pressure. Other fruits and plant extracts have not produced the same result.”
Our search of the medical literature suggests that she is right about the size of the blood pressure benefit from blueberries.
But other polyphenol-rich foods – olive oil, tea, strawberries, grapes, and more – have either been shown to lower blood pressure to a lesser extent, or exert to similar beneficial effects in arteries.
Polyphenols may help control blood sugar, too
The polyphenols in berries – and other foods – also appear to help moderate blood sugar.
Epidemiological (population) studies suggest that higher intakes of anthocyanins – the major type of polyphenols in berries – reduce fasting insulin levels and insulin resistance.
And two small clinical trials support those indications: see “Berries Seen to Balance Blood Sugar”and “Berries Fight Sugar Spikes”.
If these indications are borne out by larger clinical trials, it could mean that berries – and other whole, unrefined foods rich in polyphenols – are major allies against diabetes.
While it's not entirely clear how polyphenols help control blood sugar, the evidence points to various effects:
- Moderate glucose release from the liver
- Stimulate insulin secretion from pancreatic beta cells
- Reduce glucose (blood sugar) absorption in the intestines
- Impair the key carbohydrate-digesting enzyme, called amylase
- Modulate intracellular signaling pathways and gene expression
- Activate insulin receptors and glucose uptake in insulin-sensitive tissues
Stay tuned for updates on berries and health … and in the meantime, eat more berries!
Sources – polyphenols and blood sugar
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Sources – polyphenols and blood pressure
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