About one in three individuals have elevated blood pressure. This is bad news because hypertension is one of the most important risk factors for cardiovascular events like strokes and heart attacks. Luckily, there are many highly effective approaches for treating elevated blood pressure (diet, life-style, medication, etc.), and the drug management of hypertension has improved over the last few decades.

But unfortunately all anti-hypertensive drugs have side-effects and some patients look towards so-called alternative medicine (SCAM) to normalise their blood pressure. Therefore, we have to ask: are SCAMs effective treatments for hypertension? Because of the prevalence of hypertension, this is a question of great importance for public health.

In 2005, I addressed the issue by publishing a review entitled ‘Complementary/alternative medicine for hypertension: a mini-review‘. Here is its abstract:

Many hypertensive patients try complementary/alternative medicine for blood pressure control. Based on extensive electronic literature searches, the evidence from clinical trials is summarised. Numerous herbal remedies, non-herbal remedies and other approaches have been tested and some seem to have antihypertensive effects. The effect size is usually modest, and independent replications are frequently missing. The most encouraging data pertain to garlic, autogenic training, biofeedback and yoga. More research is required before firm recommendations can be offered.

Since the publication of this paper, more systematic reviews have become available. In order to get an overview of this evidence, I conducted a few simple Medline searches for systematic reviews (SRs) of SCAM published between 2005 and today. I included only SRs that were focussed on just one specific therapy as a treatment of just one specific condition, namely hypertension (omitting SRs with titles such as ‘Alternative treatments for cardiovascular conditions’). Reviews on prevention were also excluded. Here is what I found (the conclusions of each SR is quoted verbatim):

1. A 2020 SR of auricular acupressure including 18 RCTs: The results demonstrated a favorable effect of auricular acupressure to reduce blood pressure and improve sleep in patients with hypertension and insomnia. Further studies to better understand the acupoints and intervention times of auricular acupressure are warranted.
2. A 2020 SR of Chinese herbal medicines (CHM) including 30 studies: CHM combined with conventional Western medicine may be effective in lowering blood pressure and improving vascular endothelial function in patients with hypertension.
3. A 2020 SR of Tai chi including 28 RCTs: Tai Chi could be recommended as an adjuvant treatment for hypertension, especially for patients less than 50 years old.
4. A 2020 SR of Tai chi including 13 trials: Tai chi is an effective physical exercise in treating essential hypertension compared with control interventions.
5. A 2020 SR of Tai chi including 31 controlled clinical trials: Tai Ji Quan is a viable antihypertensive lifestyle therapy that produces clinically meaningful BP reductions (i.e., 10.4 mmHg and 4.0 mmHg of SBP and DBP reductions, respectively) among individuals with hypertension.
6. A 2020 SR of pycnogenol including 7 trials:  the present meta-analysis does not suggest any significant effect of pycnogenol on BP.
7. A 2019 SR of Policosanol including 19 studies: Policosanol could lower SBP and DBP significantly; future long term studies are required to confirm these findings in the general population.
8. A 2019 SR of dietary phosphorus including 14 studies: We found no consistent association between total dietary phosphorus intake and BP in adults in the published literature nor any randomized trials designed to examine this association.
9. A 2019 SR of ginger including 6 RCTs: ginger supplementation has favorable effects on BP.
10. A 2019 SR of corn silk tea (CST) including 5 RCTs: limited evidence showed that CST plus antihypertensive drugs might be more effective in lowering blood pressure compared with antihypertensive drugs alone.
11. A 2019 SR of blood letting including 7 RCTs: no definite conclusions regarding the efficacy and safety of BLT as complementary and alternative approach for treatment of hypertension could be drew due to the generally poor methodological design, significant heterogeneity, and insufficient clinical data.
12. A 2019 SR of Xiao Yao San (XYS) including 17 trials: XYS adjuvant to antihypertensive drugs maybe beneficial for hypertensive patients in lowering BP, improving depression, regulating blood lipids, and inhibiting inflammation.
13. A 2019 SR of Chinese herbal medicines including 9 RCTs: Chinese herbal medicine as complementary therapy maybe beneficial for postmenopausal hypertension.
14. A 2019 Cochrane review of guided imagery including 2 trials: There is insufficient evidence to inform practice about the use of guided imagery for hypertension in pregnancy.
15. A 2019 Cochrane review of acupuncture including 22 RCTs: At present, there is no evidence for the sustained BP lowering effect of acupuncture that is required for the management of chronically elevated BP.
16. A 2019 SR of wet cupping including 7 RCTs: no firm conclusions can be drawn and no clinical recommendations made.
17. A 2019 SR of transcendental meditation (TM) including 9 studies: TM was associated with within-group (but not between-groups) improvements in BP.
18. A 2019 SR of yoga including 49 trials: yoga is a viable antihypertensive lifestyle therapy that produces the greatest BP benefits when breathing techniques and meditation/mental relaxation are included.
19. A 2018 SR of mindfulness-based stress reduction (MBSR) including 5 studies: The MBSR program is a promising behavioral complementary therapy to help people with hypertension lower their blood pressure
20. A 2018 SR of beetroot juice (BRJ) including 11 studies: BRJ supplementation should be promoted as a key component of a healthy lifestyle to control blood pressure in healthy and hypertensive individuals.
21. A 2018 SR of taurine including 7 studies: ingestion of taurine at the stated doses and supplementation periods can reduce blood pressure to a clinically relevant magnitude, without any adverse side effects.
22. A 2018 SR of acupuncture including 30 RCTs: there is inadequate high quality evidence that acupuncture therapy is useful in treating hypertension.
23. A 2018 SR of co-enzyme Q10 including 17 RCTs: CoQ10 supplementation may result in reduction in SBP levels, but did not affect DBP levels among patients with metabolic diseases.
24. A 2018 SR of a traditional Chinese formula Longdanxiegan decoction (LDXGD) including 9 trials: Due to poor methodological quality of the included trials, as well as potential reporting bias, our review found no conclusive evidence for the effectiveness of LDXGD in treating hypertension.
25. A 2018 SR of viscous fibre including 22 RCTs: Viscous soluble fiber has an overall lowering effect on SBP and DBP.
26. A 2017 SR of yoga breathing exercise (pranayama) including 13 studies: The pranayama’s effect on BP were not robust against selection bias due to the low quality of studies. But, the lowering BP effect of pranayama is encouraging.
27. A 2017 SR of dietary nitrate supplementation including 13 trials: Positive effects of medium-term dietary nitrate supplementation on BP were only observed in clinical settings, which were not corroborated by more accurate methods such as 24-h ambulatory and daily home monitorings.
28. A 2017 SR of Vitamin D supplementation including 8 RCTs: vitamin D is not an antihypertensive agent although it has a moderate SBP lowering effect.
29. A 2017 SR of pomegranate including 8 RCTs: The limited evidence from clinical trials to date fails to convincingly show a beneficial effect of pomegranate on blood pressure
30. A 2017 SR of ‘forest bathing’ including 20 trials:  This systematic review shows a significant effect of Shinrin-yoku on reduction of blood pressure.
31. A 2017 SR of Niuhuang Jiangya Preparation (NHJYP) including 12 RCTs: Our review indicated that NHJYP has some beneficial effects in EH patients with liver-yang hyperactivity and abundant phlegm-heat syndrome.
32. A 2017 SR of Chinese medicines (CM) including 24 studies: CM might be a promising approach for the elderly with isolated systolic hypertension, while the evidence for CM employed alone was insufficient.
33. A 2017 SR of beetroot juice including 22 RCTs: Our results demonstrate the blood pressure-lowering effects of beetroot juice and highlight its potential NO₃-independent effects.
34. A 2017 SR of blueberry including 6 RCTs: the results from this meta-analysis do not favor any clinical efficacy of blueberry supplementation in improving BP
35. A 2016 Cochrane review of co-enzyme Q10 including 3 RCTs: This review provides moderate-quality evidence that coenzyme Q10 does not have a clinically significant effect on blood pressure.
36. A 2016 SR of Nigella sativa including 11 RCTs: short-term treatment with N. sativa powder can significantly reduce SBP and DBP levels.
37. A 2016 SR of vitamin D3 supplementation including 30 RCTs: Supplementation may be beneficial at daily doses >800 IU/day for <6 months in subjects ≥50 years old.
38. A 2016 SR of anthocyanin supplementation including 6 studies: results from this meta-analysis do not favor any clinical efficacy of supplementation with anthocyanins in improving blood pressure.
39. A 2016 SR of flaxseed including 15 trials: This meta-analysis of RCTs showed significant reductions in both SBP and DBP following supplementation with various flaxseed products.
40. A 2016 SR of massage therapy including 9 RCTs: This systematic review found a medium effect of massage on SBP and a small effect on DBP in patients with hypertension or prehypertension.
41. A 2015 SR of massage therapy including 24 studies: There is some encouraging evidence of massage for essential hypertension.
42. A 2015 SR of transcendental meditation (TM) including 12 studies: an approximate reduction of systolic and diastolic BP of -4.26 mm Hg (95% CI=-6.06, -2.23) and -2.33 mm Hg (95% CI=-3.70, -0.97), respectively, in TM groups compared with control groups.
43. A 2015 SR of Zhen Wu Decoction (ZWD) including 7 trials: This systematic review revealed no definite conclusion about the application of ZWD for hypertension due to the poor methodological quality, high risk of bias, and inadequate reporting on clinical data.
44. A 2015 SR of acupuncture including 23 RCTs: Our review provided evidence of acupuncture as an adjunctive therapy to medication for treating hypertension, while the evidence for acupuncture alone lowing BP is insufficient.
45. A 2015 SR of xuefu zhuyu decoction (XZD) including 15 studies: This meta-analysis provides evidence that XZD is beneficial for hypertension.
46. A 2015 SR of Shenqi pill including 4 RCTs: This systematic review firstly provided no definite evidence for the efficacy and safety of Shenqi pill for hypertension based on the insufficient data.
47. A 2015 SR of Jian Ling Decoction (JLD) including 10 trials: Owing to insufficient clinical data, it is difficult to draw a definite conclusion regarding the effectiveness and safety of JLD for essential hypertension.
48. A 2015 SR of Chinese herbal medicines (CHM) including 5 trials: No definite conclusions about the effectiveness and safety of CHM for resistant hypertension could be drawn.
49. A 2015 SR of Chinese medicines (CM) including 27 RCTs: When combined with Western medines, CM as a complementary treatment approach has certain effects for the control of hypertension and protection of target organs.
50. A 2015 SR of berberine including 17 RCTs: This study indicates that berberine has comparable therapeutic effect on type 2 DM, hyperlipidemia and hypertension with no serious side effect.
51. A 2015 SR of garlic including 9 double-blind trials: Although evidence from this review suggests that garlic preparations may lower BP in hypertensive individuals, the evidence is not strong.
52. A 2015 SR of chlorogenic acids (CGAs) including 5 studies: CGA intake causes statistically significant reductions in systolic and diastolic blood pressures.
53. A 2014 SR of omega-3 fatty acid supplementation including 70 RCTs:  provision of EPA+DHA reduces systolic blood pressure, while provision of ≥2 grams reduces diastolic blood pressure.
54. A 2014 SR of green tea including 20 RCTs: Green tea intake results in significant reductions in systolic blood pressure
55. A 2014 SR of probiotics including 9 studies: consuming probiotics may improve BP by a modest degree, with a potentially greater effect when baseline BP is elevated, multiple species of probiotics are consumed, the duration of intervention is ≥8 weeks, or daily consumption dose is ≥10(11) colony-forming units.
56. A 2014 SR of yoga including 17 trials: The evidence for the effectiveness of yoga as a treatment of hypertension is encouraging but inconclusive.
57. A 2014 SR of yoga including 7 RCTs: very low-quality evidence was found for effects of yoga on systolic and diastolic blood pressure.
58. A 2014 SR of yoga including 120 studies: yoga is an effective adjunct therapy for HPT and worthy of inclusion in clinical guidelines.
59. A 2014 SR of moxibustion:  a beneficial effect of using moxibustion interventions on KI 1 to lower blood pressure compared to antihypertensive drugs.
60. A 2014 SR of acupuncture including 4 sham-controlled RCTs: acupuncture significantly lowers blood pressure in patients taking antihypertensive medications.
61. A 2014 SR of Tuina including 7 RCTs: The findings from our review suggest that Tuina might be a beneficial adjuvant for patients with EH
62. A 2014 SR of ‘kidney tonifying’ (KT) Chinese herbal mixture including 6 studies: Compared with antihypertensive drugs alone, KT formula combined with antihypertensive drugs may provide more benefits for patients with SH.
63. A 2014 SR of Tongxinluo capsule including 25 studies : There is some but weak evidence about the effectiveness of TXL in treating patients with hypertension.
64. A 2014 SR of moxibustion including 5 RCTs: no confirm conclusion about the effectiveness and safety of moxibustion as adjunctive treatment for essential hypertension could be made
65. A 2013 SR of Qi Ju Di Huang Wan (QJDHW) including 10 RCTs: QJDHW combined with antihypertensive drugs might be an effective treatment for lowering blood pressure and improving symptoms in patients with essential hypertension.
66. A 2013 SR of yoga including 17 studies: Yoga can be preliminarily recommended as an effective intervention for reducing blood pressure.
67. A 2013 SR of Tianma Gouteng Yin (TGY) including 22 RCTs: No confirmed conclusion about the effectiveness and safety of TGY as adjunctive treatment for essential hypertension … could be made.
68. A 2013 SR of Zhen Gan Xi Feng Decoction (ZGXFD) including 6 RCTs: ZGXFD appears to be effective in improving blood pressure and hypertension-related symptoms for EH
69. A 2013 SR of Tianmagouteng decoction including 9 RCTs: Tianmagouteng decoction can decrease both systolic and diastolic blood pressure.
70. A 2013 SR of fish oil including 17 RCTs: The small but statistically significant effects of fish-oil supplements in hypertensive participants in this review have important implications for population health and lowering the risk of stroke and ischaemic heart disease.
71. A 2013 SR of acupuncture including 35 RCTs: While there are some evidences that suggest potential effectiveness of acupuncture for hypertension, the results were limited by the methodological flaws of the studies.
72. A 2013 SR of yoga including 6 studies: There is some encouraging evidence of yoga for lowering SBP and DBP.
73. A 2012 SR of spinal manipulation therapy (SMT) including 10 studies: There is currently a lack of low bias evidence to support the use of SMT as a therapy for the treatment of
74. A 2012 SR of vitamin C including 29 trials: In short-term trials, vitamin C supplementation reduced SBP and DBP.
75. A 2012 SR of magnesium supplementation including 22 trials: magnesium supplementation appears to achieve a small but clinically significant reduction in BP, an effect worthy of future prospective large randomised trials using solid methodology.
76. A 2012 SR of Banxia Baizhu Tianma Decoction (BBTD) including 16 RCTs: There is encouraging evidence of BBTD for lowering SBP, but evidence remains weak.
77. A 2012 SR of Liu Wei Di Huang Wan (LWDHW) including 6 RCTs: LWDHW combined with antihypertensive drugs appears to be effective in improving blood pressure and symptoms in patients with essential hypertension.
78. A 2012 SR of aromatherapy including 5 studies: The existing trial evidence does not show convincingly that aromatherapy is effective for hypertension.
79. A 2012 empty Cochrane review: As no trials could be identified, no conclusions can be made about the role of TGYF in the treatment of primary hypertension.
80. A 2012 SR of yoga including 10 studies: Not only does yoga reduce high BP but it has also been demonstrated to effectively reduce blood glucose level, cholesterol level, and body weight, major problems affecting the American society.
81. A 2011 SR of L-arginine including 11 RCTs: This meta-analysis provides further evidence that oral L-arginine supplementation significantly lowers both systolic and diastolic BP.
82. A 2011 SR of soy isoflavones including 14 RCTs: Soy isoflavone extracts significantly decreased SBP but not DBP in adult humans, and no dose-response relationship was observed.
83. A 2010 SR of moxibustion including 4 RCTs: There is insufficient evidence to suggest that moxibustion is an effective treatment for hypertension.
84. A 2010 SR of acupunctures including 20 studies: Because of the paucity of rigorous trials and the mixed results, these findings result in limited conclusions. More rigorously designed and powered studies are needed.
85. A 2010 SR of cupping including 3 trials: the evidence is not significantly convincing to suggest cupping is effective for treating hypertension.
86. A 2010 empty Cochrane review: There is insufficient evidence to support the benefit of Roselle for either controlling or lowering blood pressure in patients with hypertension.
87. A 2009 SR of acupuncture including 11 RCTs: the notion that acupuncture may lower high BP is inconclusive.
88. A 2008 SR of transcendental meditation including 9 studies: The regular practice of Transcendental Meditation may have the potential to reduce systolic and diastolic blood pressure by approximately 4.7 and 3.2 mm Hg, respectively.
89. A 2008 SR of relaxation therapies including 25 trials:  the evidence in favour of a causal association between relaxation and blood pressure reduction is weak.
90. A 2007 SR of qigong including 12 RCTs: There is some encouraging evidence of qigong for lowering SBP, but the conclusiveness of these findings is limited.
91. A 2007 SR of co-enzyme Q10 including 12 trials: coenzyme Q10 has the potential in hypertensive patients to lower systolic blood pressure by up to 17 mm Hg and diastolic blood pressure by up to 10 mm Hg without significant side effects.
92. A 2007 SR of stress reduction programs including 106 studies: Available evidence indicates that among stress reduction approaches, the Transcendental Meditation program is associated with significant reductions in BP.
93. A 2006 Cochrance review of magnesium supplementation including 12 RCTs:  the evidence in favour of a causal association between magnesium supplementation and blood pressure reduction is weak and is probably due to bias.
94. A 2006 Cochrane review of calcium supplementation including 13 RCTs: evidence in favour of causal association between calcium supplementation and blood pressure reduction is weak and is probably due to bias.

ALMOST 100 NEW SRs!

To be honest, if I had known the volume of the material, I would probably not have tackled this task. Since the publication of my mini-review in 2005, there has been an explosion of similar papers:

• 1 in 2005
• 2 in 2006
• 3 in 2007
• 2 in 2008
• 1 in 2009
• 4 in 2010
• 2 in 2011
• 8 in 2012
• 8 in 2013
• 12 in 2014
• 12 in 2015
• 6 in 2016
• 9 in 2017
• 7 in 2018
• 12 in 2019

As this is based on very simple Medline searches, the list is certainly not complete. Despite this fact, several conclusions seem to emerge:

1. There is no shortage of SCAMs that have been tested for hypertension.
2. Most seem to have positive effects; in many cases, they seem too good to be true.
3. Many of the SRs are of poor methodological quality, based on poor quality primary studies, published in less than reputable journals. Some SRs, for instance, include studies without a control group which is likely to lead to false-positive overall conclusions about the effectiveness of the SCAM in question.
4. In recent years, there are more and more SRs by Chinese authors focussed on Chinese herbal mixtures that are unknown and unobtainable outside China. These SRs are invariably based on studies published in Chinese language in journals that are inaccessible. This means it is almost impossible for the reader, reviewer or editor to check their accuracy. The reliability of the conclusions of these SRs must therefore be doubted.
5. Most of the primary studies included in the SRs lack long-term data. Thus the usefulness of the SCAM in question is questionable.
6. With several of the SCAMs, the dose of the treatment and treatment schedule is less than clear. For instance, one might ask how frequently a patient should have acupuncture to control her hypertension.
7. Some of the SCAMs assessed in these SRs seem of doubtful practicality. For instance, it might not be feasible nor economical for patients to receive regular acupuncture to manage their blood pressure.
8. Several contradictions emerge from some of the SRs of the same modality. This is particularly confusing because SRs are supposed to be the most reliable type of evidence. In most instances, however, the explanation can easily be found by looking at the quality of the SRs. If SRs are based on uncontrolled studies, or if they fail to critically evaluate the reliability of the included primary trials, they are likely to arrive at conclusions that are too positive. Examples for such confusion are the multiple SRs of co-enzyme Q10 or the three yoga SRs of 2014.
9. Because of this confusion, SCAM advocates are able to select false-positive SRs to support their opinion that SCAM is effective.
10. Despite a substantial amount of positive evidence, none of the SCAMs have become part of the routine in the management of hypertension. A 2013 statement by the American Heart Association entitled Beyond medications and diet: alternative approaches to lowering blood pressure: a scientific statement from the american heart association concluded that it is reasonable for all individuals with blood pressure levels >120/80 mm Hg to consider trials of alternative approaches as adjuvant methods to help lower blood pressure when clinically appropriate. A suggested management algorithm is provided, along with recommendations for prioritizing the use of the individual approaches in clinical practice based on their level of evidence for blood pressure lowering, risk-to-benefit ratio, potential ancillary health benefits, and practicality in a real-world setting. 

What lessons might this brief overview of SRs teach us? I think the following points are worth considering:

• Systematic reviews are the best type of evidence we have for estimating the effectiveness of treatments. But it is essential that they include a strong element of CRITICAL evaluation of the primary studies. Without it, a SR is incomplete and potentially counter-productive.
• The primary studies of SCAM are far too often of poor quality. This means that researchers should thrive to improve the rigour of their investigations.
• Both poor-quality primary studies and uncritically conducted SRs are prone to yielding findings that are too good to be true.
• Editors and reviewers have a responsibility to prevent the publication of trials and SRs that are of poor quality and thus likely to mislead us.
• Those SCAMs that have shown promising effects on hypertension (for instance Tai chi) should now be submitted to further independent scrutiny to find out whether their efficacy and usefulness can be confirmed, for instance, by 24-h ambulatory and daily home blood pressure monitoring and studies testing their acceptability in real life settings. Subsequently, we ought to determine whether the SCAM in question can be reasonably integrated in routine blood pressure management.
• The adjunctive use of a SCAM that has been proven to be effective and practical seems a reasonable approach. Yet, it requires proper scientific scrutiny.
• There is a paucity of cost-effectiveness studies and investigations of the risks of SCAM which needs to be addressed before any SCAM is considered for routine care.