In this special feature, we collate some of the most intriguing hypertension studies from 2019. We particularly focus on nutrition, risk factors, and hypertension's relationship with dementia.
Today, in the United States, around 1 in 3 adults has high blood pressure, which doctors also call hypertension.
Hypertension increases the risk of cardiovascular events, such as stroke and coronary disease, and, if doctors don't treat it, it can reduce lifespan.
Because it is worryingly prevalent, and because the physical ramifications can be significant, scientists are plowing a great deal of effort into understanding hypertension.
Although people first identified hypertension as a medical condition thousands of years ago, scientists are still picking away at the details.
Research that scientists completed in 2019 has thrown out some exciting and, in some cases, unexpected findings. For instance, a paper appearing in February concluded that, for women over 80 years of age, having "normal" blood pressure had an increased risk of mortality when compared with individuals with high blood pressure.
Elsewhere, Greek scientists concluded that napping might help reduce blood pressure. "Midday sleep appears to lower blood pressure levels at the same magnitude as other lifestyle changes," explains one of the researchers, Dr. Manolis Kallistratos.
Another surprising study, which scientists presented at the 83rd Annual Scientific Meeting of the Japanese Circulation Society, concluded that needing to urinate multiple times at night might be a sign of hypertension.
The role of nutrition
The food that we eat has a huge impact on our overall health; that goes without saying. The America Heart Association, for instance, suggest that eating a diet rich in fruits and vegetables and avoiding products with high levels of salt and fat can help keep blood pressure in check.
Over the past few years, interest in nutrition, in general, has skyrocketed. More and more, scientists are focusing on individual foods or food compounds that can directly benefit health. So, although poor diet is a well-known risk factor for hypertension, researchers in 2019 drilled down deeper.
Specific foods and supplements
One study appearing in 2019 investigated the impact of consuming walnuts on blood pressure. It concluded that the individuals who ate an experimental walnut-heavy diet experienced a significant reduction in blood pressure.
In these types of studies, it is worth digging a little deeper; often, industry or organizations who might stand to benefit from positive results are funding them. The walnut study above, for instance, was partly funded by the California Walnut Commission.
This observation does not mean that we should dismiss the results out of hand, but it provides pause for thought.
Another recent study concentrated on spirulina, which is the dried biomass of a bacterium called Spirulina platensis. Manufacturers can add it to foods, and some people take it as a supplement.
Earlier experiments hinted at spirulina's potential to reduce hypertension, and in the most recent study, they attempted to find out why this might be.
The scientists concluded that a protein that the digestion of spirulina produces causes blood vessels to relax. The authors hope that this protein, known as SP6, might one day be useful in the treatment of hypertension.
Preservatives, additives, and water
Rather than focus on specific foods, a further study looked at the impact of buying food from local retailers rather than supermarkets.
The authors theorized that by eating local produce, individuals would avoid consuming the various preservatives and additives that keep food "fresh" over long distances.
Although the study was relatively small, the authors found that after 6 months, those who consumed local produce had lower levels of visceral fat, improved depression scores, and reduced systolic blood pressure.
Approaching from a different angle, a team of scientists recently asked whether drinking water that is high in minerals might reduce blood pressure.
To investigate, they focused on people living in a coastal region of Bangladesh. Drinking water there varies in salinity. In areas of high salinity, the water contains greater quantities of sodium, which we know increases blood pressure. However, the same water also includes more magnesium and calcium, both of which reduce blood pressure.
The authors concluded that higher salinity levels decreased blood pressure overall; they write that "the [blood pressure]-lowering effects of [calcium] and [magnesium] counteracted the harmful effects of [sodium].
Causes and risk factors
Some risk factors for hypertension are fairly well established; they include drinking excessive amounts of alcohol, smoking tobacco, stress, and obesity. However, because high blood pressure is so common, there are likely to be many more factors at play.
Similarly, although scientists know which lifestyle and dietary factors influence blood pressure, they are not entirely sure how they cause the changes.
Understanding why and how blood pressure arises in some people and not others is essential and could, potentially, lead to innovative ways of treating or preventing hypertension.
Some scientists are exploring possible risk factors which, at face value, seem unlikely. For instance, one paper, appearing in the Journal of Public Health in June, examined the role of where people live.
Earlier studies found an association between exposure to air pollution and hypertension risk, and this latest work confirms those earlier suspicions and takes it a step further.
As expected, the researchers found a relationship between air pollution and hypertension; however, the increase in risk was only significant for those who were living in multi-family homes, such as blocks of flats.
The authors believe that this might be due to several factors, for instance, living in close quarters with other people may be more stressful or more noisy. This study provides a glimpse of the complex realm of potential elements that might influence blood pressure.
Bizarrely, one group of scientists recently investigated how mouthwash might influence hypertension risk.
Publishing their findings in the journal Frontiers in Cellular and Infection Microbiology, the authors conclude that mouthwash kills "good bacteria" in the mouth. These good bacteria produce nitric oxide (NO), which is important for blood vessel health.
NO acts as a vasodilator, which means it causes the muscles that line blood vessels to relax, thereby widening the vessels and reducing blood pressure.
In particular, the scientists concentrated on the chemical chlorhexidine, which they found in some mouthwashes.
According to the authors, they demonstrated that "twice-daily chlorhexidine usage was associated with a significant increase in systolic blood pressure after 1 week of use, and recovery from use resulted in an enrichment in nitrate-reducing bacteria on the tongue."
Still focusing on the oral region, a 2019 review looked for links between gum disease and hypertension. They showed that individuals with severe periodontitis — a form of gum disease — had a 49% increased risk of hypertension.
Senior author Prof. Francesco D'Aiuto explains their results in a nutshell: "We observed a linear association — the more severe periodontitis is, the higher the probability of hypertension."
The role of zinc
Another project investigated the role of zinc in maintaining blood pressure at healthy levels. Over the years, researchers have noted links between low zinc levels and an increased risk of high blood pressure, but the precise mechanism has been tough to pin down.
The latest research identified the key player in this interaction between zinc and blood pressure; according to the authors, the sodium chloride cotransporter (NCC) in the kidney is the lynchpin. The NCC is responsible for pumping sodium back into the body, thereby preventing it from being excreted in the urine.
Zinc interacts with the NCC: when zinc is present, the NCC is less active, meaning that the body retains less sodium. This is important because high sodium levels — from consuming too much salt, for instance — are factors in increasing the risk of hypertension.
The authors hope that this new knowledge will help improve treatment and write:
"Understanding the specific mechanisms by which [zinc deficiency] contributes to [blood pressure] dysregulation may have an important effect on the treatment of hypertension in chronic disease settings."
Hypertension and dementia
Scientists have identified a relationship between hypertension and vascular dementia. The association makes sense because vascular dementia can occur following stroke, and hypertension is a risk factor for stroke.
However, it also appears that hypertension might increase the risk of other types of dementia, including Alzheimer's disease.
A study appearing in June this year found that a common blood pressure drug — nilvadipine — slowed the progress of Alzheimer's disease by improving blood flow in the brain.
Specifically, the research team showed that people who took the medication had a 20% increase in blood flow in the hippocampus, a brain region vital for memory and learning, in comparison to those who did not take nilvadipine.
Patterns throughout life
Other scientists have looked at fluctuations in blood pressure and their possible role in dementia. For instance, one investigation that recruited participants who were living with Alzheimer's disease found that the condition progressed quicker in those whose blood pressure fluctuated most.
"More fluctuations [in blood pressure] might affect whether cognitive function declines more slowly or rapidly."
Senior author Dr. Jurgen Claassen
With a similar theme, another group of scientists observed the pattern of blood pressure across decades. The authors summarize their findings:
"[A] pattern of sustained hypertension from middle to late life and a pattern of midlife hypertension followed by late-life hypotension were associated with an increased risk for subsequent dementia, compared with participants who maintained normal blood pressure."
Another project that charted hypertension over a lifespan found that individuals with high or rising blood pressure between 36 and 53 years of age were more likely to have white matter lesions and a smaller brain volume in later life.
The authors hope that these findings will inspire both doctors and the public to check and take charge of their blood pressure sooner rather than later.
As 2020 rolls into view, hypertension is sure to stay high on the medical research agenda. As science gradually untangles hypertension's causes and mechanisms, managing and minimizing this highly prevalent condition must draw ever closer.
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