Is ‘really low’ urine pH a health hazard?

Dear Dr. Roach: I have a friend who’s 28 with “really low” urine pH. Apparently, it is due to constant dehydration and drinking coffee all day long, to the point that the doctor recommended that he drink lots of water with lemon.

That sounds counterintuitive to me. I recall you mentioning before that the body maintains a fairly constant pH. Does that also apply to urine? Could you please comment on urine pH? — K.S.

The body maintains a very constant pH of the blood at a slightly alkaline 7.4 (7 is neutral; below 7 is acidic, above 7 is alkaline). Even a few tenths of a point higher or lower and the body is in severe trouble.

The primary method the body uses to regulate blood pH is by increasing or decreasing carbonic acid loss through breathing out more or less carbon dioxide, but the kidneys play their part by adjusting urine pH. The urine pH cannot get much below 4.5 due to limitations of the kidney.

It is counterintuitive that consuming lemon juice, which is a quite strong acid, will cause the urine to become less acidic. This is because citric acid is metabolized to bicarbonate, which is alkaline and excreted in the urine. Nephrologists use this effect in people with calcium oxalate stones.

If your friend has normal kidneys, a change in diet away from meat and with more plants will make the urine pH less acidic.

There are a host of unusual causes. The ones making the urine pH acidic are quite uncommon, and they include Cushing’s syndrome and excess licorice ingestion. Licorice contains glycyrrhizic acid, which acts like a hormone on the kidney to affect urine pH. Coffee has no consistent effect on urine pH, but dehydration can make urine more acidic. It is unlikely your friend will develop medical issues due to low urine pH.