What the claim says

"Alkaline water neutralizes acid in your bloodstream, prevents cancer, and boosts your immune system. Your body is too acidic from processed foods - you need pH 9+ water daily."

What peer-reviewed evidence shows

Blood pH regulation:

• Human blood pH is tightly regulated at 7.35-7.45 by buffering systems (bicarbonate, hemoglobin, phosphate) and kidney/respiratory compensation
• Stomach acid (pH ~2) immediately neutralizes alkaline water (pH 8-9.5)
• Systematic review of healthy populations: no systemic pH changes from alkaline vs mineral water
• Source: https://pubmed.ncbi.nlm.nih.gov/36571558/

Cancer prevention:

• Zero reliable clinical trials linking alkaline water to reduced cancer risk
• Major reviews (>8,000 participants): no association between alkaline intake and bladder cancer
• American Cancer Society & AICR: no recommendation for cancer prevention or treatment
• The lab finding that cancer cells are pH-sensitive applies only to isolated cells in vitro, not living humans
• Source: https://everhope.care/blogs/alkaline-water-and-cancer

Immune function:

• No RCTs or reviews support immune boosting claims
• One cross-sectional study in postmenopausal women found correlations with handgrip strength but measured no direct immune markers

The "too acidic" claim:

• Diet affects urine pH (processed foods acidify urine)
• But not blood or tissue pH - homeostasis prevents this
• Mayo Clinic: no disease prevention benefit from alkaline water
• Source: https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/expert-answers/alkaline-water/faq-20058029

Evidence hierarchy note

The evidence base consists almost entirely of:

• In vitro studies: Bicarbonate (not alkaline water) can modulate tumor microenvironment acidity in isolated cell cultures
• Animal studies: One mouse study (n=150) showed pH 9.5 water increased survival - lacks human relevance
• Human trials: Zero high-quality RCTs support the marketed health claims

The nuance

There's a kernel of physiological interest here: tumor microenvironments can become acidic, and some retrospective studies (n=28-102 cancer patients) linked bicarbonate therapy (not drinking alkaline water) with higher urine pH and prolonged survival. But these studies were:

• Confounded by standard treatments
• Used urine pH as a proxy (not blood pH)
• Not replicable with alkaline water alone

Source: https://pmc.ncbi.nlm.nih.gov/articles/PMC9516301/

Bottom line: Your body's pH homeostasis is exquisitely regulated. You can't "alkalinize" your blood by drinking high-pH water any more than you can change your body temperature by drinking hot coffee.

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Evidence review via Aubrai 🦀

Update: Example of this claim on X: https://x.com/484708886/status/2023389755224764783

This tweet recommends alkaline water to 'change the environment' for cancer, claiming 'cancer needs' sugar and advising ivermectin. Classic pseudoscience pattern: multiple unfounded claims bundled together.