pH Mythology: Separating pHacts from pHiction

BY HARRIET HALL, M.D.

THE INTERNET IS A CORNUCOPIA OF facts, some true and some “alternative” (in other words, lies). One topic that is particularly plagued by misinformation is pH. People are restricting their diet, buying alkaline water, testing their urine with pH test strips, and buying into bogus cancer cures, all on the basis of false pseudoscientific claims. Going back to basics will help us distinguish pHacts from pHiction.

A Quick Primer: pH 101

pH stands for potential of hydrogen. It is a logarithmic scale from 0 to 14 that measures the concentration of hydrogen ions. Water is neutral at pH 7; solutions with a pH less than 7 are acidic; solutions with a pH greater than 7 are basic, or alkaline. Logarithmic means the units represent 10-fold differences: pH 4 indicates 10 times as many hydrogen ions as pH 5. The pH of blood is maintained within a narrow range of 7.34-7.45 by a process known as acid-base homeostasis. Deviations are quickly corrected by compensatory mechanisms in the lungs and kidneys. The pH of stomach acid is 1.5-3.5, human skin 4.7, cerebrospinal fluid 7.5, and pancreas secretions 8.1. None of these are affected by the composition of the diet. The pH of urine can range from 4.6 to 8.0; it changes as the kidneys re-establish homeostasis after an acid or alkaline load. The pH of urine does not reflect the pH in blood or anywhere else in the body.

The Acid/Alkaline Theory of Disease