Hawthorn: An Herb that Helps Hypertension

By David Kiefer, MD. Dr. Kiefer is a Clinical Instructor, Family Medicine, University of Washington, Seattle; Clinical Assistant Professor of Medicine, University of Arizona, Tucson, and Adjunct Faculty at Bastyr University, Seattle; Dr. Kiefer reports no financial relationships relevant to this field of study.

An integrative approach to high blood pressure ventures into many realms, including herbal medicine. For supporting cardiovascular health and treating heart disease, hawthorn is a botanical treatment that often comes to mind. It is best known for treating congestive heart failure, but researchers have recently taken a clue from decades of use by herbalists, eclectic physicians, and integrative health care providers, to study its use in hypertension. This article will update you about current research, botany, and physiology.

History and Traditional Use

Hawthorn has been used as a medicine for centuries. As far back as the thirteenth century, hawthorn was used for nausea, vomiting, diarrhea, and other gastrointestinal problems, a constellation of symptoms that is similar to its use in Traditional Chinese Medicine.1 In Europe in the late eighteenth century, hawthorn began to be used for heart troubles. This use is thought to have first surfaced in the United States in 1896.1

Many different groups of Native Americans used several species of hawthorn as foods and medicines, including haw (Crataegus douglasii, C. pruinosa, and C. submollis), black haw (C. douglasii), dotted haw (C. punctata), red haw (C. chrysocarpa, C. columbiana), and black hawberry (Crataegus sp.). Examples of the medical uses include infusions of the twigs for side pain and bladder troubles, decoctions of the berries as a laxative as well as to treat diarrhea, roots for consumption, and infusions of the root bark for general debility.2

Botany and Pharmacology

Hawthorn, also known as English hawthorn, haw, and maybush, is a shrub or small tree, and this common name refers to several plant species used medicinally, including Crataegus laevigata (also called C. oxyacantha or C. oxyacanthoides) and C. monogyna, all of which are in the rose, or Rosaceae, family.1,3 The plant parts most often mentioned for their medicinal effects are the leaves, flowers, and berries; the latter are most often red. Hawthorn is found in Europe, Asia, and North America.1

Hawthorn contains numerous physiologically-active phytochemicals which differ in concentration within the different plant parts. The oligomeric procyanidins, including procyanidin B-2, are found in highest concentration in the leaves, whereas the flavonoids (quercetin, hyperoside) and flavone-C-glycosides (vitexin, orientin) are most prevalent in flowers.3 Hawthorn also contains amines, catechols, carboxylic acids, and triterpenes such as crataegus acid.1,3

Mechanism of Action

The oligomeric procyanidins in hawthorn are thought to have a hypotensive action by decreasing peripheral vascular resistance,4 though other compounds, such as the crataegus acids, affect the vascular system by dilating coronary blood vessels.1 The flavonoid compounds are also thought to have vasodilatory activity, perhaps through the activation of endothelium-derived relaxing factor and inhibition of phosphodiesterase.1

Hawthorn contains numerous compounds with antioxidant activity, especially the flavanols epicatechin and proanthocyanidin B2, as well as other flavonoids, such as hyperoside, rhamnoside, and rutin.5 These compounds are found in different concentrations, depending on the plant part, as well as the type of extraction (water, methanol, ethanol, etc.) used.

Using a rat model, researchers investigated the hypotensive effects of hawthorn. The investigators extracted leaves of Crataegus tanacetifolia (a species found in Turkey) with several different solvents, and then administered this extract orally to hypertensive rats (created through nitrous oxide (NO) inhibition), comparing them to saline control groups and to a group treated with the isolated hawthorn flavonoid hyperoside.6 The hyperoside-treated group showed prevention of NO-inhibition hypertension at week 4. From these results, as well as pathology specimens, the researchers concluded that there is a possible increase in renal nitrous oxide synthetase activity that would accounting for hawthorn's hypotensive action.

Clinical trials

Hawthorn's best documented clinical effect is for heart failure [HF]).7 Many of these studies were conducted in Europe, and secondary outcomes commonly included the measurement of blood pressure.1,8 For example, in studying the effect of various hawthorn extracts on NYHA functional class II HF, an uncontrolled trial found a decrease in systolic blood pressure of 5.9 mmHg, and a decrease in diastolic blood pressure of 2.2 mmHg, while randomized trials have documented statistically significant decreases in mean diastolic blood pressure during exercise, as well as decreases in systolic blood pressure from 171 mmHg to 164 mmHg.1

A few other trials focused on the hypotensive effect for hawthorn. For example, thirty-six people with mild hypertension (diastolic blood pressure 85-100) were randomized in a double-blind trial to 10 weeks of either 600 mg magnesium amino acid chelate, 500 mg of hawthorn (aqueous-alcoholic extract of hawthorn leaves and flowers, standardized to 1.8% vitexin-2-rhamnosides), magnesium plus hawthorn, or placebo.4 Subjects were not on any antihypertensive medicine. During the research trial, blood pressure measurements were taken at baseline, five weeks, and ten weeks; no significant differences were found between any of the groups, though the authors mention that the extract used was on the lower end of the dosage recommendation, and the duration of the trial may not have been long enough to show an effect.

Another trial compared 16 weeks of placebo to 1200 mg daily of an extract of dried hawthorn flowering tops (Crataegus laevigata, C. oxyacantha) in 79 people with type 2 diabetes and hypertension.9 The patients were recruited from a medical practice in England, and allowed to take their regular medicines for hypertension and diabetes; exclusions were heart disease or major pathology, and pregnancy. An intention-to-treat analysis revealed that the hawthorn group had a slightly lower diastolic blood pressure (2.6 mmHg, P = 0.035). Systolic blood pressure and glycemic control was the same between both groups. The authors also concluded that hawthorn was safe, causing no changes in liver or kidney function, nor any significant side effects.

Hawthorn species from other countries are also being studied for their effect on blood pressure. Iranian hawthorn (Crataegus curvisepala) was found to lower blood pressure when compared to placebo in 92 people with mild hypertension after receiving a water-ethanol extract of hawthorn leaves and flowers three times daily for three months (P < 0.05).10

Dosages and Forms

Water infusions (using dried flowers or leaves) or decoctions (using dried berries) of hawthorn are generally dosed at 1.5-3.5 grams daily.1 Some research trials and other sources mention the use of extracts standardized to a percentage of flavonoid or oligomeric procyanidins; these are sometimes preferred because there is variation in phytochemical concentration depending on the plant part and preparation method, which can be avoided with the use of standardized products. Focusing on these latter recommendations, hawthorn would be dosed in a wide range of 160-900 mg daily (divided into two or three doses) of a water-ethanol extract of the leaves and flowers; this would equal approximately 30-169 mg of epicatechin or 3.5-20 mg of flavonoids.1 HF dosing is 12-15 mg of hyperoside daily (300-900 mg of dried extract) or 45-90 mg of oligomeric procyanidins (240-560 mg of dried extract); it is unclear whether or not these are the best doses for the treatment of hypertension.

Adverse Effects, Contraindications, and Drug Interactions

Hawthorn is generally well-tolerated and is associated with neither frequent nor serious adverse effects, though some clinical trials don't mention adverse effects and, in other cases, an exact cause-effect relationship is difficult to establish.11 However, higher doses can cause gastrointestinal upset, headache, rash, diaphoresis, palpations, insomnia, and dizziness.1,11 Hawthorn may enhance the effect of other antihypertensives or herbal medicines with cardiovascular effects.12

A systematic review of hawthorn's adverse effects examined 24 trials involving 5,577 patients.11 The doses ranged from 160-1800 mg over 3-24 weeks; the most common preparations were WS 1442 and LI 132. Most of the 166 adverse events reported were mild, as mentioned above.

Concerns about hawthorn's possible effects on p-glycoprotein function and interaction with pharmaceuticals (ie, digoxin) that also affect p-glycoprotein prompted a 10-day study on eight healthy volunteers randomized to either digoxin 0.25 mg or digoxin plus a standardized extract of hawthorn leaves and flowers (WS 1442, 450 mg twice daily).13 The pharmacokinetic parameters were the same for both groups, presumably indicating that there was not a significant interaction between hawthorn and digoxin.

Hawthorn is not recommended for pregnant or lactating women, nor children under the age of 12.1

Conclusion

Hawthorn consists of several different species that are used medicinally. Most of these species have well-documented traditional use for a variety of medical conditions, including cardiovascular problems such as hypertension. The physiological effects of hawthorn stem primarily from oligomeric procyanidins and flavonoids; the former decreases peripheral vascular resistance while the latter appears to dilate vessels by activating endothelium-derived relaxing factor and inhibiting phosphodiesterase. Other postulated mechanisms involve renal nitrous oxide synthetase activity and antioxidant effect. There are many published clinical trials evaluating the benefit of hawthorn in heart failure, and some of these trials also documented a slight hypotensive effect (2-6 mmHg). Clinical trials specifically focusing on hypertension showed no effect, a modest effect just on diastolic blood pressure, and benefits in both the systolic and diastolic blood pressures. Recommended doses vary widely, but many experts prefer water-ethanol extracts standardized to one or more of the active phytochemicals. Hawthorn is generally well-tolerated and considered safe, given its long history not only as a medicine but also a food; there are but few serious complications, contraindications, and interactions to be aware of.

Recommendation

Research to date demonstrates only a very modest effect on blood pressure; this remains to be definitively proven by well-designed clinical trials, but the effects do not seem to be clinically important. Despite preliminary in vitro research showing a variety of physiological effects from the phytochemicals in hawthorn, and a positive safety profile, its main clinical indication remains mild-to-moderate heart failure.

References

1. Rigelsky JM, Sweet BV. Hawthorn: Pharmacology and therapeutic uses. Am J Health Syst Pharm. 2002;59:417-422.

2. Moerman DE. Native American Ethnobotany. Portland, Oregon: Timber Press; 1998

3. Mills S, Bone K. Principles and Practice of Phytotherapy. Edinburgh: Churchill Livingstone; 2000

4. Walker AF, et al. Promising hypotensive effect of hawthorn extract: A randomized double-blind pilot study of mild, essential hypertension. Phytother Res. 2002;16:48-55.

5. Bahorun T, et al. Antioxidant activities of Crataegus monogyna extracts. Planta Med. 1994;60:323-328.

6. Kocyildiz ZC, et al. Crataegus tanacetifolia leaf extract prevents L-NAME-induced hypertension in rats: A morphological study. Phytother Res. 2006;20:66-70.

7. Pittler MH, et al. Hawthorn extract for treating chronic heart failure: Meta-analysis of randomized trials. Am J Med. 2003;114:665-674.

8. Schmidt U, et al. Efficacy of the hawthorn preparation LI 132 in 78 patients with chronic congestive heart failure defined as NYHA functional class II. Phytomedicine. 1994;1:17-24.

9. Walker AF, et al. Hypotensive effects of hawthorn for patients with diabetes taking prescription drugs: A randomised controlled trial. Br J Gen Pract. 2006;56:437-443.

10. Asgary S, et al. Antihypertensive effect of Iranian Crataegus curvisepala Lind: A randomized, double-blind study. Drugs Exp Clin Res. 2004;30:221-225.

11. Daniele C, et al. Adverse-event profile of Crataegus spp: A systematic review. Drug Saf. 2006;29:523-535.

12. Brinker F. Herb Contraindications and Drug Interactions. Sandy, Oregon: Eclectic Medical Publications; 2001

13. Tankanow R, et al. Interaction study between digoxin and a preparation of hawthorn (Crataegus oxyacantha). J Clin Pharmacol. 2003;43:637-642.