Systematic review of the association between dietary acid load, alkaline water and cancer

Abstract

Objectives To evaluate the evidence for a causal relationship between dietary acid/alkaline and alkaline water for the aetiology and treatment of cancer.

Design A systematic review was conducted on published and grey literature separately for randomised intervention and observational studies with either varying acid–base dietary intakes and/or alkaline water with any cancer outcome or for cancer treatment.

Outcome measures Incidence of cancer and outcomes of cancer treatment.

Results 8278 citations were identified, and 252 abstracts were reviewed; 1 study met the inclusion criteria and was included in this systematic review. No randomised trials were located. No studies were located that examined dietary acid or alkaline or alkaline water for cancer treatment. The included study was a cohort study with a low risk of bias. This study revealed no association between the diet acid load with bladder cancer (OR=1.15: 95% CI 0.86 to 1.55, p=0.36). No association was found even among long-term smokers (OR=1.72: 95% CI 0.96 to 3.10, p=0.08).

Conclusions Despite the promotion of the alkaline diet and alkaline water by the media and salespeople, there is almost no actual research to either support or disprove these ideas. This systematic review of the literature revealed a lack of evidence for or against diet acid load and/or alkaline water for the initiation or treatment of cancer. Promotion of alkaline diet and alkaline water to the public for cancer prevention or treatment is not justified.

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Strengths and limitations of this study

• Broad search of both the published and unpublished literature on both alkaline diets and alkaline water was conducted for studies to include in this systematic review.

• We located only one observational study that fit the inclusion criteria.

• The objective, to determine if evidence of a causal relationship exists between dietary acid or alkaline and the etiology of cancer and/or the treatment of this disease, was defined a priori.

• Explicit reproducible methodology.

• Assessed the included study's validity, ie risk of bias, using a quality checklist.

Introduction

The general public is being encouraged by the lay press that to prevent cancer; they are persuaded to assess the acidity of their urine and/or saliva as an assessment of the acidity of their body and then to modify their diets accordingly.1–7 The alkaline diet, or acid–ash diet, is being promoted based on the claims that modern diets acidify the body1–11 causing diseases including cancer, osteoporosis and cardiovascular disease.1–12 The alkaline diet is also promoted for conditions including diabetes and hypertension. Promoters of this diet claim that changing food choices to more ‘alkaline’ selections prevents all of these conditions1–9 ,11 and has the ability to treat cancer once it has been developed.5 ,10 ,12 ,13 This diet is based on the concept that mineral components of foods make the body acidic, alkaline or neutral.14

The alkaline diet is designed to provide more alkaline ions after metabolism, based on the acid–ash hypothesis developed over 100 years ago.15 The acid–ash hypothesis suggests that to achieve a more alkaline load, one must consume more fruit and vegetables with only a moderate intake of protein. While marketing of this diet implies that the diet changes will raise systemic pH, a well-conducted randomised trial of these diet changes altered only systemic pH by 0.014 units, while the urine pH increased by 1.02 units.16 This study reveals that diet changes can alter urine pH but does not change blood pH.16 Furthermore, the fact that the effect of phosphorus on calcium metabolism is opposite to that was predicted by the hypothesis17 raises questions about the validity of the hypothesis. Additionally, a review of the body of evidence regarding the acid–ash/alkaline hypothesis for bone health found that the hypothesis is not supported and there is no evidence that altering the diet acid load improves bone health.18

The marketing of the alkaline diet promotes not only a diet, but also the sale of related supplements and water alkaliniser machines through almost every media medium, including websites, books and videos.1–6 ,8 In our experience, patients with cancer are approached by salespeople who are promoting water alkalinisers as a way to treat their cancer. Studies suggest that a substantial and growing number of patients use the internet to obtain health information,19 ,20 which may not be innocuous. Oncologists report that internet use by patients with cancer contributes to confusion and anxiety among patients with cancer.20

There is some evidence that some cancer cells and tumours grow well in an acidic environment in the laboratory.21 ,22 While the alkaline diet is being promoted to correct the acid state that the modern diet creates, the American Institute of Cancer Research and the Canadian Cancer Society have stated that the body tightly regulates systemic pH and food choices will only affect urine pH and not body acidity.23 ,24 Studies show that while urine pH changes in response to diet changes, blood pH does not.16 ,25 As acid/base forming potential of foods does alter urinary pH,16 ,25 cancers of the urinary tract may be an important focus in investigating claims of the alkaline diet to prevent and treat cancer.

As far as we are aware, no systematic review has been done to evaluate the evidence for an association between dietary acid and/or alkaline, or the effectiveness of alkaline water, for the aetiology or treatment of cancer. The purpose of this systematic review is to conduct an extensive search of the published and unpublished literature to determine whether evidence of a causal relationship exists between dietary acid or alkaline and the aetiology of cancer and/or the treatment of this disease.

Methods

Eligibility criteria

Randomised interventions and observational human studies of acid–base intakes of diet, supplemental salts to change systemic pH (such as potassium bicarbonate or potassium citrate) and consumption of alkaline water, with cancer outcomes (both aetiology and treatment), were sought. No language or publication date restrictions were imposed. Human participants of all ages and backgrounds were considered. Studies with no original research (narrative reviews, editorials) and non-human studies were excluded from this review.

Literature search

Two reviewers conducted independent literature searches, one with the assistance of a librarian (J.P.), in an attempt to find all human studies of the ash–acid diet hypothesis or an alkaline diet with any type of cancer as the outcome. Studies were identified through search text words and Medical subject headings: diet, dietary, acid, acidic, alkaline, acid-base, acid-base equilibrium, acid-ash, net acid excretion (NAE), ‘potential renal acid load, water, cancer, neoplasm’ (see online supplementary file). For published literature, databases searched included Ovid MEDLINE, PubMed, Cochrane Register of Clinical Trials, CINAHL and Embase up to April 2015. No limits were applied to searches, and studies reported in all languages were considered. In an effort to include all available studies, reference lists for the located articles were also reviewed. For grey literature, Current Controlled Trials, Canadian Cancer Trials, Google, and Google Scholar were manually searched up to April 2015.