For how we live.
For most healthy adults the measured difference is small. But side-sleeping has real evidence in three specific situations: nocturnal reflux, obstructive sleep apnoea and late pregnancy.
Two things you do in bed have randomised evidence for nocturnal reflux: raising the head of the bed cut acid exposure from 21% to 15%, and a device that kept people on their left side nearly doubled treatment success.
The popular claim is that a shot before meals fires up digestion. The controlled measurement shows vinegar slows the stomach down — helpful for blood sugar, unhelpful if you already digest slowly.
Bringing up milk is normal in healthy babies: it peaks around four months and usually fades by the first birthday. Most infants need no medicine, and the evidence for acid-suppressing drugs in simple reflux is weak.
A double-blind trial gave 17,598 people pantoprazole or placebo for three years and tracked pneumonia, fractures, kidney disease and dementia. Only gut infections rose, and only modestly.
Observational studies had linked proton pump inhibitors to fractures, dementia, kidney disease and more. A randomised trial collected all of those outcomes and found only enteric infections.