Introduction

Hypertension, or high blood pressure, is an increasingly prevalent condition worldwide. In 2021, the World Health Organization (WHO) has reported that around 1.28 billion adults aged 30-79 years worldwide have hypertension, and less than half have it diagnosed and treated [1]. Some complications of high blood pressure include cardiovascular diseases such as heart attacks and strokes [1]. Often dubbed as the ‘silent killer’, this condition often shows no signs and symptoms [1].

Blood pressure reading is mainly divided into 2 numbers [2]:

• Systolic blood pressure (i.e., the top number): this number indicates the pressure your blood is exerting against the blood vessels’ walls when the heart beats
• Diastolic blood pressure (i.e., the bottom number): this number indicates the pressure your blood is exerting against the blood vessels’ walls when the heart relaxes between beats

With the incidence of hypertension on the rise, there is also an increasing awareness of how diet and other means can help with lowering the blood pressure naturally (i.e., without the use of medications). The implications of using dietary fiber and their effects on blood pressure has garnered interest [3]. How does the use of dietary fiber help with lowering blood pressure? Does the fiber affect blood pressure directly or through other mechanisms, such as via its interactions with the gut microbiota?

World Hypertension Day falls on 17 May every year. In conjunction with this day, find out how the health of your gut and dietary fiber intake is implicated in your blood pressure readings!

How Fiber Intake affects Blood Pressure

Fiber is a form of carbohydrates, naturally present in plants. Although most carbohydrates can be broken down by the body’s enzyme into simple sugars, our body is unable to completely break down fibers and gets passed through to the large intestine. It is generally divided into 2 forms: soluble and insoluble fibers [4].

The use of fiber to reduce blood pressure has been studied and published in various clinical trials. A meta-analysis done in 2005 aggregated data from 24 different studies and trials to see the effects of fiber on blood pressure [5]. This study found that fiber supplementation at 11.5g per day caused a non-significant decrease in systolic blood pressure and a significant change in diastolic blood pressure, with effects larger for older and hypertensive populations [5].

The authors of the study also concluded that increasing fiber intake in the general population may contribute to prevention of hypertension [5], especially as the intake of dietary fiber in the general population is low [6]. A high-fiber diet was also found to have experienced a 15% reduction in systolic blood pressure, along with an inverse risk of developing cardiovascular diseases [7].

How Gut Microbiota affects Blood Pressure

The effects of fiber on blood pressure lowering may have also been due to the presence of the microorganism environment in the gut, which is also termed as your gut microbiota. The gut microbiota consists of a range of microorganisms consisting of bacteria, virus, and fungi [8], and the composition differs depending on several factors such as environmental and lifestyle reasons (e.g., diet) [9].

The gut microbiota ferments the undigested fiber that passes through to the large intestine, producing short-chain fatty acids (SCFAs) and gases. These SCFAs produced by the breakdown of fiber by the gut microbiota play important roles in multiple body functions, one of which includes the modulation of blood pressure and decreasing the risk of developing hypertension from a fiber-rich diet [10]. Dysbiosis of the gut (i.e., alterations of the gut microbiota) is also found to be linked with hypertension [11].

There are many mechanisms on how the gut microbiota and its derivatives affect the blood pressure [12]:

• SCFAs produced from the fermentation of the fibers activates receptors that play a part in blood pressure regulations
• Reduction in microbial gene richness may also lead to inflammation, which can also be a cause of high blood pressure
• Gut microbiota can influence the production of chemicals by gastrointestinal cells, which has effects on the gut-brain axis
• Gut microbiota may also regulate genes related to immunity, inflammation and metabolism which may also affect blood pressure

Conclusion

Hypertension, often termed as the ‘silent killer’, often presents with no symptoms, and affects more than 1 billion of adults worldwide. It has severe complications if it goes undetected and untreated, including heart attacks and strokes. There has been much interest in natural ways such as the use of diet and dietary fiber in managing and lowering blood pressure. The use of fiber has also been touted to be able to reduce blood pressure, with potential effects due to the gut microbiota. Importance of the gut microbiota on blood pressure could also have been mediated by other factors such as its effects on the immunity and metabolism of the individual.

This article is written in conjunction with World Hypertension Day, which falls on 17 May every year.

References

1. World Health Organisation. Hypertension. 2021 August. Available on: https://www.who.int/news-room/fact-sheets/detail/hypertension
2. American Heart Association (AHA). Understanding Blood Pressure Readings. Available on: https://www.heart.org/en/health-topics/high-blood-pressure/understanding-blood-pressure-readings
3. High-Fiber Diet May Fight High Blood Pressure. 2005. Available on: https://www.webmd.com/hypertension-high-blood-pressure/news/20050304/high-fiber-diet-may-fight-high-blood-pressure
4. Fiber. Available on: https://fibrosol.com/fiber/
5. Streppel MT, Arends LR, van ’t Veer P, et al. Dietary Fiber and Blood Pressure: A Meta-analysis of Randomized Placebo-Controlled Trials. Arch Intern Med. 2005;165(2):150–156. Available on: https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/486375
6. Hartley L, May MD, Loveman E, et al. Dietary fibre for the primary prevention of cardiovascular disease. Cochrane Database Syst Rev. 2016;2016(1):CD011472. Available on: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7032538/
7. EurekAlert! Science News Release. American College of Cardiology. High fiber diet associated with reduced CV risk in hypertension, type 2 diabetes patients. 2019 Oct. Available on: https://www.eurekalert.org/news-releases/717892
8. Thursby E, Juge N. Introduction to the human gut microbiota. Biochem J. 2017;474(11):1823-1836. Available on: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5433529/
9. Rutsch A, Kantsjö JB., Ronchi F. The Gut-Brain Axis: How Microbiota and Host Inflammasome Influence Brain Physiology and Pathology. Immunol. 2020;11. Available on: https://www.frontiersin.org/articles/10.3389/fimmu.2020.604179/full
10. Richards E.M., Pepine C.J., Raizada M.K. et al. The Gut, Its Microbiome, and Hypertension. Curr Hypertens Rep. 2017;19:36. Available on: https://link.springer.com/article/10.1007/s11906-017-0734-1
11. Yang T, Santisteban MM, Rodriguez V, et al. Gut dysbiosis is linked to hypertension. Hypertension. 2015 Jun;65(6):1331-40. Available on: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4433416/
12. Jose PA, Raj D. Gut microbiota in hypertension. Curr Opin Nephrol Hypertens. 2015;24(5):403-409. Available on: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4578629/