By Dr. Hanisha Patel, ND
Introduction
About 25% of Americans die of cardiovascular diseases (CVD) every year.
Heart failure is responsible for 11 million physician visits each year and more hospitalizations than all forms of cancer combined (CDC, 2013). High blood pressure, high cholesterol, and smoking are all risk factors of cardiovascular diseases. Diseases that are considered cardiovascular diseases include but are not limited to hypertension, pulmonary hypertension, chronic heart failure, coronary artery disease, peripheral artery disease, atrial fibrillation, aortic aneurysm, cardiomyopathy, myocardial infarcts, hypercholesterolemia, and stroke. Thirty percent of patients with acute heart failure are re-hospitalized within 60-90 days.6 Given the scope of this problem, it would be of great benefit to widen our array of interventions to aid this large population of people.
Cadmium, lead, and arsenic are toxic metals that are non-essential to human existence. Cadmium has been shown to be associated with increased risk of renal dysfunction, osteoporosis, cancer, and cardiovascular diseases. There is an increased level of cadmium in smokers because tobacco accumulates cadmium from soil.2 Lead is a toxic metal that is still ubiquitous in our world today. Lead accumulation has been shown to be associated with an increased risk of elevated systolic blood pressure, coronary heart disease (CHD), stroke, and PAD.4 Inorganic arsenic is a naturally occurring toxic metal that can be found in chicken, rice, and groundwater. In epidemiologic studies, high-chronic arsenic exposure has been linked to CVD, including CHD, stroke, and PAD.3
Many toxic metals, including cadmium, lead, arsenic, and mercury, are excreted via sweat. Circulation can be enhanced by increasing the thermal load on the body allowing sweating to occur.7 Waon therapy (WT), a form of sauna therapy that translates to soothing warmth in Japanese, is a far infrared-ray dry sauna. WT is where the entire body is warmed in an evenly heated chamber for 15 min at a temperature that soothes mind and body, allowing the body temperature to increase 1.0-1.2 °C. Following the heated chamber, soothing warmth is sustained by maintaining warmth at rest for an additional 30 min. Fluids are supplied at the end to replace loss from perspiration.1 Another method of sauna therapy researched for patients with CHF included 10 far-infrared (FIR) sauna sessions over 14 days for 15 minutes at 60°C followed by 30 minutes of bed rest covered by a blanket.8
This literature review will discuss the potential therapeutic benefits of sauna therapy for patients with CVD due to heavy metal exposure.
Methods
PubMed, ClinicalKey, and Science Direct were the databases utilized for this search with no restriction on date, type of study, nationality, or language. The initial search terms included “cardiovascular disease AND sauna.” The following search terms included “cadmium in sweat,” “cadmium and cardiovascular disease,” “lead and cardiovascular disease,” “heavy metals in sweat,” and “arsenic and cardiovascular disease.” These items were searched due to the relevance of this review having to do with heavy metal exposure in relation to CVD and diminishing risk with sauna therapy. The resulting 30 studies were narrowed down to 17 by language, availability, and relevance.
Six of the articles found in the search were systematic reviews of previous studies. Five of the articles included studies done with patients with CHF, two of the articles were about studies done on PAD, and one of the articles was on a study with patients with hypertension. Four of the articles were on cadmium, lead, arsenic, and mercury. One of the articles consisted of a case study. One article in this review disputes the hypothesis that toxic elements can be excreted via sweat. Two of the articles included mice in their studies and the rest were done on human subjects. The two articles found on mice studies were discarded for this review. All of the articles in this review were done on human subjects with CVD and included patients who were concurrently on conventional therapy and had been diagnosed with a cardiovascular condition by a physician.
Results
Heavy metals and CVD. Borné et al discussed cadmium exposure and its effects on cardiovascular health leading to CHF and atrial fibrillation (AF). Blood samples were donated, and cadmium could be measured in 4378 people with conventional cardiovascular risk factors and biomarkers. Patients were followed from baseline examination between March 1991 and September 1996 in Malmö, Sweden until death, emigration from Sweden, or December 2010. Cadmium toxicity was found to be associated with CHF but not AF.2
One systematic review discussed lead exposure and its effects on CVD. This review included studies that used biomarkers to determine lead levels in blood, bone, or other specimens, environmental measures, or indirect measures such as living, job exposure, etc. Cardiovascular risk factors included those with reported clinical cardiovascular end points such as BP, CHD, stroke, or PAD and intermediate cardiovascular end points such as left ventricular mass, heart rate, heart rate variability, or electrocardiographic abnormality. In general populations, lead exposure was positively associated with clinical cardiovascular endpoints in all studies reviewed. In occupational populations, including those who work in battery, ceramic, pigment, and smelter industries, mortality was higher among workers with a greater number of years of employment. However, relative risk estimates across occupational studies varied widely, with positive, inverse, and null associations. This review found an association between lead exposure and blood pressure with populations in different geographic, ethnic, and socioeconomic backgrounds.4
One systematic review discussed arsenic exposure and its effects on CVD. Pooled relative CVD risk estimates were calculated separately for those with high levels of arsenic exposure. For CHD, stroke, and PAD, dose-response trends were evaluated in each study. Most studies were conducted in high arsenic exposure areas of Taiwan, Bangladesh, Chile, Inner Mongolia, and Pakistan. Most studies were assessed using indirect measures or using environmental measures. Most studies used CVD mortality endpoints to assess CVD outcomes. This review found an association between high arsenic exposure areas and CVD, CHD, PAD, and stroke.3
Sjögren et al discussed a case-controlled study involving mercury exposure and its effects on CVD. The case included a comprehensive study of 6784 male and 265 female workers from four mercury mines and mills in Spain, Slovenia, Italy, and Ukraine. Findings in Slovenia revealed increase in mortality due to ischemic heart disease among men. Duration of employment was positively correlated with mortality from ischemic heart disease.5
“Cadmium, lead, arsenic, and mercury have been shown to depress nitric oxide (NO) availability, increase oxidation and inflammation, increase endothelial dysfunction, and induce cell death. These are all significant findings in CVD.”
One systematic review discussed excretion of arsenic, cadmium, lead, and mercury via sweat. Studies included workers with occupational exposures and populations with no occupational exposures who were experiencing chronic ill health or were in good health. Arsenic was found to be higher in sweat than in blood plasma. Cadmium excretion was noted to be higher in sweat than in urine. Lead excretion was found to be higher in sweat than in urine. When measuring levels of mercury, sweat mercury levels varied; but there was no correlation with mercury urine levels.7
CVD and sauna therapy. Two of the articles were randomized controlled trials (RCT) of patients with CHF.1,9 Fujita et al included 40 patients with symptomatic CHF, left ventricular ejection fraction (LVEF) <50% on echocardiography, and New York Heart Association (NYHA) functional classes II or III.9 Patients were split into two groups, one of which did sauna therapy once a day, five days a week, for four weeks. The populations assessed by the articles were adults (18+) diagnosed with either CHF and/or PAD with no significant differences in body weight, heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), cardiothoracic ratio (CTR), LVEF, BNP, and uric acid between groups. There was significant improvement in body weight, CTR, and BNP and echocardiography revealed an increase LVEF following four weeks of sauna therapy. These changes were not seen in the control group.9
Sobajima et al included 49 patients with previous hospitalization due to worsening of CHF, NYHA functional class ≧ II, or both. Patients were split into two groups, one of which completed sauna therapy once a day for three weeks. Results were based on evaluation of cardiac function and specific activity scale (SAS) which included brain natriuretic peptide (BNP), NYHA, and 6-minute walk distance (6MWD), flow-mediated vasodilation (FMD), natural killer (NK) cell activity, and SF-36 QOL scores. Sauna therapy improved NYHA functional class, SAS, and 6MWD, LVEF, NK cell activity, FMD, plasma BNP levels, and SF-QOL scores.1
The Shinsato study revealed sauna therapy improvement in leg pain, exercise performance, ABPI, circulating CD34+ cell numbers, and serum nitrate and nitrite levels. There were no significant changes in VEGF.19
Shinsato et al’s RCT included 21 patients with PAD. Inclusion criteria were intermittent claudication for a minimum of four weeks with no improvement with conventional treatment, resting ankle-brachial pressure index (ABPI) <0.75 in the affected limb on two consecutive examinations done weekly, and lower limb artery lesions detected with computed tomographic angiography (CTA, magnetic resonance angiography (MRA) or color duplex ultrasound. The patients were randomly divided into groups, one of which completed sauna therapy once a day, five days a week, for a total of six weeks. Results were based on evaluation of in leg pain, exercise performance, ABPI, circulating CD34+ cell numbers, serum nitrate and nitrite levels, and vascular endothelial growth factor (VEGF).10
There were very few adverse effects of sauna therapy and they were considered minor. In the Shinsato et al study, patients reported transient leg pain that subsided after a few sessions of sauna therapy.10
Discussion
The articles discussed in this literature review provide sufficient evidence to suggest sauna therapy in adjunct to conventional pharmaceutical therapeutics can be an effective form of treatment for reducing cardiovascular risk due to cadmium, lead, arsenic, and/or mercury exposure. This review provides some meaningful insights to guide future research and clinical practice. These articles reveal great promise in sauna therapy for the treatment and prevention of cardiovascular diseases such as CHF, PAD, high blood pressure, and stroke by reducing heavy metal accumulation.
Heavy metals such as cadmium, lead, arsenic, and mercury can have a significant physiologic effect. Cadmium increases the permeability of vascular endothelial monolayers by inhibiting cell proliferation and promoting cell death.11 It has also been shown to down-regulate nitric oxide (NO) mediated vasodilation.2 Lead accumulation has been shown to have an inverse relationship with estimated glomerular filtration rate (eGFR) indicating higher levels of lead can lead to reduced renal function. It has also been shown to enhance oxidative stress and impair NO-mediated vasodilation leading to increased vascular tone and peripheral vascular resistance.4 Arsenic exposure has been shown to increase inflammation, enhance oxidative stress, and endothelial and smooth muscle cell proliferation, vessel remodeling, and apoptosis.3 Mercury has been shown to increase endothelial dysfunction and reduce NO synthesis, increase oxidative stress and inflammation, and enhance mitochondrial and immune dysfunction.5 All of these mechanisms can lead to the progression of CVD.2-5
The renin angiotensin aldosterone system (RAAS) and natriuretic peptides (NPs) play key roles in the pathophysiology of CVD and CHF in particular. CHF progression leads to constant activation of the RAAS and a diminished response of NPs. This leads to increase in angiotensin II and aldosterone levels. This causes sodium reabsorption, which leads to hypertrophy and fibrosis in the heart and vasculature. Activation of the RAAS and NPs may be due to impaired NO-mediated vasodilation.
Many conventional therapies for CHF target the renin-angiotensin-aldosterone system (RAAS). Medications like angiotensin-converting enzyme inhibitors (ACEIs), angiotensin II receptor blockers (ARBs), and aldosterone-receptor blockers have significantly reduced mortality in CHF patients. Sauna therapy has been shown to enhance nitric oxide (NO) availability, decrease aldosterone, and decrease BNP and CNP activity.12 (See Figure 1) Due to these factors and the success of sauna therapy in the RCTs discussed in this review, it can be hypothesized that sauna therapy can be an effective form of treatment for CVD with concurrent use of conventional pharmaceutical therapeutics.
Complications of Studies
Borne et al utilized a self-administered questionnaire on current use of conventional CVD medications, smoking habits, and educational status. This could lead to false information due to variability in patient’s ability to remember their medications and willingness to reveal truthful information.2 The articles systematically reviewed in Navas-Acien et al did not sufficiently differentiate between classification of lead exposure and outcome and did not fully define what cardiovascular risk factors were and what other occupational exposures may have contributed to the findings.4 The articles systematically reviewed in Manuscript et al (2013) did not include proper internal comparisons between high and low arsenic exposure.3 Both of these systematic reviews only included exact measurements of lead and arsenic levels within each individual for a few of the articles.3,11 Sjögren et al only discussed one case report on mercury exposure leading to the progression of CVD and therefore cannot be used as a sufficient source to prove this correlation.5 Shinsato et al’s RCT may have some semblance of a placebo effect due to the inability to create a double-blinded RCT considering the nature of the intervention.10
All of these RCTs were conducted in conjunction with conventional pharmaceutical therapeutics that were not standardized, therefore outcomes could differ based on medications. No studies were conducted without the use of conventional pharmaceutical therapeutics, which may hinder the ability to understand the full efficacy of sauna therapy as an intervention.
Based on this discussion, the conclusion can be made that cadmium, lead, arsenic, and/or mercury toxicity are among the factors that contribute to cardiovascular disease; and since it appears these heavy metals are predominantly excreted through sweat, sauna therapy can be effective in reducing the amount of heavy metals circulating in the bloodstream.7 More research would need to be conducted on heavy metal toxicant levels in patients before and after receiving sauna therapy to definitively make this claim.
Future studies should include research with larger populations with more specific age groups. Conventional therapies were taken simultaneously, and it would be interesting to see the effects of sauna therapy while decreasing the dose of conventional treatment to see if there can be therapeutic benefit without conventional treatment. Follow up on these studies were also short- and long-term effects would need to be monitored.
This therapy should be done concurrently with modifying lifestyle factors such as diet, exercise routine, and smoking cessation. The research was all done on patients who were concurrently using conventional treatment, and this must be taken into consideration as well.
There were no conflicts of interest reported in any of the articles in this review.
Conclusion
The studies found using these search methods indicate that sauna therapy may be an appropriate form of treatment for patients with CVD and in preventing CVD from advancing to complications such as CHF and PAD.
Cadmium, lead, arsenic, and mercury have been shown to depress nitric oxide (NO) availability, increase oxidation and inflammation, increase endothelial dysfunction, and induce cell death. These are all significant findings in CVD.2-5,7 These toxic metals can be excreted via sweat and therefore excessive sweating may help to reduce the amount of these metals circulating in the bloodstream.2,7
It is evident from the studies reviewed that 15 minutes of sauna therapy for at least five days a week for three to six weeks is able to reverse the adverse effects of heavy metal toxicity by enhancing nitric oxide (NO) availability, decreasing aldosterone, decreasing oxidation and inflammation, reducing endothelial dysfunction, and assisting with mitochondrial function.6,7,12 Considering heavy metal toxicity can play a role in the development of these conditions, it can be concluded that sauna therapy can help decrease levels of heavy metals such as cadmium, arsenic, lead, and mercury, and therefore improve prognosis of patients with cardiovascular diseases.
Acknowledgements:
This literature review was edited by Dr. Debrah Harding and Dr. Baljit Khamba.
Biography
Dr. Hanisha Patel received a Bachelor of Science degree in pharmaceutical sciences at Ohio State University. Following her undergraduate career, she worked for an NGO in Pune, India, where she worked with women in rural and slum areas. She then received her degree in naturopathic medicine from Bastyr University California where she continued to work with underserved communities locally and globally. As a naturopathic doctor, she specializes in cardiovascular diseases, diabetes, women’s health, and neurodegenerative diseases. When she is not working with patients, she enjoys traveling, dancing, hiking, HIIT workouts, yoga, and watching sunsets.
References
1. Sobajima M, et al. Waon Therapy Improves Quality of Life as Well as Cardiac Function and Exercise Capacity in Patients With Chronic Heart Failure. International Heart Journal. 2014; 56(2), 203–208.
2. Borné Y, et al. Cadmium exposure and incidence of heart failure and atrial fibrillation: A population-based prospective cohort study. BMJ Open. 2015;5(6):1–8.
3. Moon K, Guallar E, Navas-Acien A. Arsenic Exposure and Cardiovascular Disease: An Updated Systematic Review. Curr Atheroscler Rep. December 2012:14(6), 542–555.
4. Navas-Acien A, et al. Lead exposure and cardiovascular disease – A systematic review. Environmental Health Perspectives. 2007;115(3), 472–482.
5. Sjögren B, Holme J, Hilt B. Mortality from cardiovascular diseases and exposure to inorganic mercury. Occupational and Environmental Medicine 2002;59(7): 494.
6. Miyata M, Tei C. Waon Therapy for Cardiovascular Disease: Circulation Journal. 2010;74(4), 617–621.
7. Sears ME, Kerr KJ, Bray RI. Arsenic, cadmium, lead, and mercury in sweat: A systematic review. Journal of Environmental and Public Health. 2012. http://doi.org/10.1155/2012/184745
8. Crinnion WJ. Sauna as a valuable clinical tool for cardiovascular, autoimmune, toxicant- induced and other chronic health problems. Alternative Medicine Review : A Journal of Clinical Therapeutic. 2011;16(3): 215–25.
9. Fujita S, et al. Effect of Waon Therapy on Oxidative Stress in Chronic Heart Failure. Circulation Journal. 2011;75(2), 348–356.
10. Shinsato T, et al. Waon therapy mobilizes CD34+ cells and improves peripheral arterial disease. Journal of Cardiology. 2010;56(3):361–366.
11. Tellez-Plaza M, et al. Cadmium Exposure and Incident Cardiovascular Disease. Epidemiology. May 2013; 24(3), 421–429. http://doi.org/10.1097/EDE.0b013e31828b0631.Cadmium
12. Fukushima A, Kinugawa S. Renin-Angiotensin-Aldosterone System and Natriuretic Peptides as Possible Targets of Waon Therapy in Heart Failure. Circulation Journal. 2017; 81(5), 635–636.
