Blueberries are trending in social media and the general media today following the publication of a brand new study on blueberries by researchers from Kings College, London (1).
According to an editorial in the New York Times, the 'blue' in blueberries makes them 'super berries' which can reduce mortality from some diseases by up to 20%. I do like to read the New York Times but when it comes to health matters, I prefer to check out the source data for myself.
In this article, we will look at the details behind this new study along with a general review of the science behind these so-called 'super blue blueberries'.
What are Blueberries?
Blueberries are one of the most popular berries in the USA (2).
Blueberries are also known as arandano and bleuet. They belong to the genus Vaccinium and the family Ericaceae.
In some countries, the terms blueberries and bilberry are used interchangeably (2). This is technically incorrect as they are different fruits.
Blueberries typically contain (per 100gm):
- Water 84.21 gm
- Energy 57 kcal
- Protein 0.74 gm
- Fat 0.33 gm
- Carbohydrate 14.49 gm
- Fiber 2.4 gm
- Sugar 9.96 gm
- Calcium 6 mg
- Iron 0.28 mg
- Magnesium 6 mg
- Phosphorus 12 mg
- Potassium 77 mg
- Sodium 1 mg
- Zinc 0.16 mg
- Vitamin C 9.7 mg
- Thiamin 0.037 mg
- Riboflavin 0.041 mg
- Niacin 0.418 mg
- Vitamin B 6 0.052 mg
- Folate 6 mcg
- Vitamin B 12 0
- Vitamin A 54 IU
- Vitamin E 0.57 mg
- Vitamin D 0 and
- Vitamin K 19.3 mcg (3).
The berries are enjoyed for their taste and are also used for health benefits in cancer, memory issues, blood pressure, diabetes, depression and bladder infections (4).
Blueberries are relatively unique among fruits as they contain five of the major anthocyanidins (cyanidin, delphinidin, malvidin, peonidin, and petunidin). (5).
The 'blue' in blueberries comes from the anthocyanin content which is the basis of the current interest in blueberries today as we will discuss in a later section in this article.
Is There any Research?
There are over 1700 publications on Blueberries which includes 71 clinical trials. To put this into context, there are over 3000 publications on strawberries which includes over 100 clinical trials.
Do They Support Digestion?
The effect of blueberry plus grape juice versus placebo as add-on therapy in people undergoing standard treatment for peptic ulcer disease failed to show any benefits of the active intervention over placebo (6).
Drinking a wild blueberry drink was found to modulate the bacterial content of the gut by increasing the specific intestinal bifidobacteria content (7). This is believed, but not proven, to ultimately lead to better health.
Inflammatory bowel disease was induced in 7 female mice by oral administration of 3% dextran sodium sulfate for 7 days (8). The question under study was whether or not blueberry extract could rescue these mice from inflammatory bowel disease under these circumstances.
Overall, it was found that blueberry extract could indeed reduce mucosal inflammation and damage and did so via a combination of anti-oxidation and down-regulation of the expression of inflammatory mediators.
There is no convincing human data to suggest that blueberries have a specific role in gut health or digestion.
Do They Alleviate Inflammation?
Chinese investigators studied the combination of blueberries plus etanercept for juvenile arthritis (9). Etanercept is an inhibitor of tumor necrosis factor and is used to treat selected cases of arthritis.
It works but it comes with some serious potential side effects eg life threatening sepsis. The study enrolled 201 patients with juvenile arthritis and randomized them to either etanercept alone, etanercept plus blueberries or etanercept plus placebo for 6 months.
The group that received the combination of etanercept plus blueberries had statistically significant improvements in symptoms and inflammatory markers along with significantly lower levels of side effects.
There is evidence to support a role for blueberries as add-on therapy in juvenile inflammatory arthritis.
Do They Help Fight Cancer?
There is a growing interest in the use of blueberries for cancer prevention and treatment (10).
Blueberries are thought to exert anti-cancer effects by blocking inflammatory molecules and cancer cell growth in addition to promoting cancer cell death (11).
Since I started writing this article, a paper has been published which suggests that laboratory experiments show that blueberries may increase the sensitivity of cervical cancer cells to radiotherapy (12). This is still at the theory stage and needs to be tested in women with cervical cancer.
A study from Kentucky showed that blueberry supplementation could prevent and treat breast cancer in an experimental rat model (13).
Despite significant interest in the area, there is no clinical evidence to support an anti-cancer role for blueberries.
Do They Promote Heart Health?
A 2016 Cochrane review of 6 randomized controlled trials with 204 participants showed no effect of blueberries on BP (14). The authors summarized their findings by stating that their data does not support any clinical efficacy of blueberry supplementation in BP control.
As we will see, this conclusion may no longer be valid and the entire dataset needs to be re-analyzed in view of the new data that we will discuss shortly.
Swedish and Spanish investigators studied a drink containing a mixture of blueberries, blackcurrants, lingonberries, strawberries, and tomatoes versus a placebo drink in 40 adults (15). The placebo drink had the same content of carbohydrates and the same pH as the berry-tomato drink.
The study was designed as a five-week cross-over study. The study focused on cognitive and cardio-metabolic factors. Cognitive tests included memory, attention and reaction time. Cardio-metabolic tests included BP, glucose, lipids, inflammatory and oxidative markers.
The berry-tomato drink was good for lipids and for memory. It had no effect on any of the other variables measured in the study. Sometimes, results that look negative can actually be positive. The berry drink did not have any effect on glucose or insulin.
Taken on its own, this could be seen as a negative result. However, when taken in context, it has clinical significance. The control group had statistically significant increases in glucose and insulin. The berry-tomato group protected against this. Kudos to the researchers for great study design and a great placebo or we would have missed this benefit.
A 2017 study showed that a single serving of blueberries improved arterial function in young adult smokers and non-smokers (16).
Now we get to the brand new data which we mentioned above (1). The study randomized 40 adults to either 7.8 gm of blueberries or placebo daily for a total duration of one month (1). The study found significant reductions in blood pressure within two hours of eating blueberries.
By the end of the study, participants in the blueberry arm of the study were noted to have an average drop in blood pressure of 5mm of mercury. This is impressive clinically. According to the research team, this is comparable to the expected effects of pharmaceutical pills.
The researchers went out to extrapolate that if people could maintain this benefit in the longterm that this could translate into a reduction in mortality of up to 20%. It has to be emphasized that the latter is merely an educated guess and is built on numerous assumptions and remains to be proven in long term clinical studies but the short-term benefits of the study are still convincing.
Blueberries have been shown to have beneficial effects on lipid levels and brand new data also shows that blueberries have beneficial effects on BP control.
Do They amp up Weight Loss?
No effect on weight was noted in the Nilson cardio-metablic risk factor study mentioned above (15).
Next, we look at a study where baby mice were fed either a normal diet or a high-fat diet for 12 weeks (17). They were also given either nothing extra, blueberry polyphenol extract or orlistat (a standard anti-obesity drug).
Not surprisingly, the high-fat diet resulted in weight gain, dysregulation (increases in lipids) of blood lipids and increased adiposity (a fancy word for fat). Both the blueberry polyphenols and orlistat arms of the study did not have weight gain or dysregulation of their lipids. Additionally, both the orlistat and the blueberry arms were noted to have changes in their gut microbiota.
The effect on the gut microbiota is very interesting as there is growing evidence that gut microbiota plays a key role in our weight and may speak to the possible mechanism of action of blueberries on weight.
We do have some clinical data. A review of dietary questionnaires administered to over 100,000 people over 24 years found a very clear inverse relationship between intake of certain fruits and weight gain (18).
This means that the intake of certain fruits can protect against weight gain. We will focus on blueberries in this article. The research study indeed showed that blueberries protected against weight gain.
There is evidence from a number of studies that blueberries can help with weight loss.
Do They Boost Cognitive Health?
There is a large body of evidence to look at here.
A double-blind cross over study in 21 children compared freeze dried blueberry powder to placebo on cognitive function (19). The children were tested using specialized tests designed to capture cognitive functioning.
Interestingly, when tested taking the blueberry supplement, the children performed faster and this was especially noticeable during complex tasks and tasks involving visual cues.
Six months of blueberry supplementation was compared to placebo on cognitive function in 122 elderly adults (20). This study is really interesting. One of the tests used was an episodic memory test where people were shown words, then twenty minutes later they were asked to recall those words which were now mixed in with a new set of words.
Some of the new sets of words were deliberately designed to be phonetically similar to the first set of words. The idea behind the design of this study was to have a test that was difficult but also to create deliberate interference by having similar words on the new list. I guess many of us work or live in environments with lots of interference and hence this study is of interest (certainly to me).
The study showed benefits in this test at three months but not six months which was a little confusing. The study included other cognitive tests but showed no benefits in the other tests. No benefits on mood were noted either.
The authors struggled to explain the fact that there were benefits noted at three months and not six months. They suggested that either the medication degraded over time or that the benefits were maxed out at the three-month mark as possible explanations.
The study did find reduced blood pressure at the three and six month follow ups which attributed to the blueberries which was interpreted as pretty much annihilating the theory that the blueberries could have degraded.
This leaves us a study with interesting results that we cannot fully explain. Nonetheless, the blueberries were found to offer some short-term benefits in terms of memory performance as compared to placebo.
Back to the BP issue. This study did show significant reductions in BP which is different from the systematic review mentioned earlier but consistent with the results of the new study from London.
(I am beginning to feel like I might need to stop to take some blueberries to improve my cognition as this is getting confusing - and of course, there is plenty of interference in the background as family life unfolds as I write).
The authors even further complicate things by reminding us that improved BP control can improve cognition. This raises the possibility that blueberries improved some aspects of cognition via an effect on BP.
A study published last year looked at freeze dried blueberries versus placebo in 37 older adults for 90 days (21). At the end of the 90 days, improvements were noted in cognition but not in gait or balance.
A study published last year from Cincinnati gave elderly women either fish oil, blueberries, fish oil plus blueberries or placebo (22). These study participants are described as having 'cognitive complaints'.
The rationale for this study design was to test two supplements that have been independently shown to have beneficial effects on cognition. Single use of either the blueberries or fish oil was associated with decreases in what was described in the study as 'cognitive complaints'.
Blueberries were associated with statistically significant improvements in cognition. Here comes the kicker. The combination of fish oil with blueberries did not improve cognition as expected. I cannot explain this finding.
There are some signals that blueberries can have beneficial effects on cognition. Bearing in mind that cognition is really complex, I can understand why different studies with different patient demographics and different designs would have different outcomes.
None of these studies enrolled thousands of people or followed people for years. We have limited data but some signals that blueberries might have some benefits in some people, though it is disconcerting that the combination of fish oil and blueberries did not work.
Do Blueberries Fight Harmful Free Radicals?
The best data on this subject comes from a clinical trial which was published in 2017 from Baton Rouge (23). Adults with the metabolic syndrome were randomized to either receive blueberry smoothies or placebo smoothies twice daily for 6 weeks.
The study showed that the blueberry based smoothies statistically significantly reduced blood levels of superoxide and total reactive oxygen species. This supports the theory that blueberries can fight free radicals.
The study also showed that caused significant changes in immune markers. Specifically, significant changes in tumor necrosis factor, interleukin and granulocyte-macrophage colony–stimulating factor. It is difficult to predict that the effects of these changes in the immune system might be.
There were increases in the tumor necrosis factor, and interleukin while the granulocyte-macrophage colony–stimulating factor decreased. Granulocyte-macrophage colony–stimulating factor boosts the growth of white cells that typically fight infections.
Blueberries have been shown to fight harmful free radicals.
Are Blueberries Safe?
There is a difference between food grade doses and therapeutic doses of foods. Eating regular food portions of blueberries should not be an issue and can be regarded as generally safe. This may not necessarily be the case with a high dose of blueberries used for medicinal purposes, although this is just a theoretical possibility.
Either way, there is insufficient information to recommend the medicinal use of blueberries in pregnancy.
Blueberries may lower blood glucose and care should be taken in people who are on blood sugar lowering tablets or injections.
Blueberries contain relatively high levels of vitamin K and can interact with warfarin or coumadin as blood thinning agents.
Like many herbal remedies, it is generally advisable that blueberry supplements should be discontinued at least two weeks before surgery.
Sometimes when I write for Healthy But Smart, I feel that the articles can sound negative. I just report on what the science says and the reality is that the science is often lacking which means that we cannot make health claims for certain foods or supplements.
That would be irresponsible. The fact that there is no evidence does not mean that the food/supplement does not work. It just means that there is no evidence.
Thankfully, blueberries are much more impressive. There is evidence to support the use of blueberries for control of weight, BP, inflammation, free radical damage, and possibly cognition. While we sometimes separate out these medical issues, the reality is that they are all interconnected.
As the paper on BP and cognition explained, benefits on BP can benefit cognition. We also know that inflammation and free radical damage can also affect cognition.
I suspect that we have only begun to unravel the effects of blueberries on the human body but I like what I am seeing so far. What does this mean in real life for me?
I am not going to try to mainline blueberries in the hope of living to be 500 years old.
When I do go to the store to buy fruits, I am more likely to pick blueberries on a regular basis.
On a final note, blueberries do not feature currently on the Dirty Dozen list which is a list of fruits and vegetables considered to have a high risk of contamination with pesticides (24).