Diarrhea is a major health problem, especially in the developing world. It is estimated that diarrheal disease is responsible for roughly 21 percent of all deaths in children younger than 5 worldwide.
In “A Meta-analysis of the Effects of Oral Zinc in the Treatment of Acute and Persistent Diarrhea,” researchers found the duration of acute and persistent diarrhea was significantly shorter when zinc was used versus placebo.
Vomiting appeared to be significantly increased with zinc treatment, though it was less frequent with zinc sulfate and acetate when compared to zinc gluconate.
The exact mechanism of zinc on the intestine is not fully known, but it could include inhibition of cAMP-induced chloride dependent fluid secretion, improved absorption of water and electrolytes, improved regeneration of intestinal epithelium , increased levels of brush border enzymes and possibly an enhancement in the immune response allowing for better clearance of pathogens.
At this point there may be enough evidence to recommend zinc in the treatment of both acute and persistent diarrhea.
The addition of zinc to oral rehydration solution appears to be less effective as also shown by this meta-analysis.
This is possibly due to oral rehydration solution already maximizing the small intestinal fluid absorption rates and the addition of zinc not providing any additional benefit.