Children from poor regions with clean water, hygiene and sanitation programs tend to be slightly taller than those who grow up in similar areas without such programs, according to a new review.

Kids ages four and younger who washed their hands, drank clean water or used well-maintained toilets - or some combination of the three - were on average 0.2 inches taller than those lacking such protocols, the findings show.

However, researchers led by Alan Dangour of the London School of Hygiene & Tropical Medicine reported that trend was not consistent among all 14 studies included in their review.

“The absolute difference in height is not large, but stunting is associated with many negative health and economic outcomes,” Dr. Anna Bowen, a medical epidemiologist at the U.S. Centers for Disease Control and Prevention, told Reuters Health in an email.

“Therefore increasing the median height of the population even slightly could have benefits,” added Bowen, who was not involved in the new review.

All 14 studies were originally designed to test the effectiveness of water, sanitation and hygiene (WASH) interventions on the prevention of diarrhea and diseases among children in low-income countries. In 2011, the U.S. and United Kingdom allocated a combined total of $626 million in aid for such interventions.

Dangour and his colleagues were interested in whether those programs had any secondary benefits on children’s height and weight.

In comparing children in regions that did and did not have the programs, they found no WASH-related benefits on weight, but a small benefit on height, according to findings published by The Cochrane Collaboration, an international organization that evaluates medical research.

Yet, when the researchers analyzed data only from randomized controlled trials - the gold standard in medicine - the benefit on height could not be found.

Each of the randomized trials included in the review lasted only nine to 12 months, they noted, a short period to see height changes. And information on nutrition was available for less than half of children across all studies.

Nearly one quarter of children under age five are short for their age as a result of undernutrition, or stunting, according to the World Health Organization.

In their analysis, the researchers did not attempt to determine whether water, sanitation or hygiene had the biggest impact.

“The whole package is important,” Dangour told Reuters Health. “So we didn’t want to separate them out.”

Bowen said although the findings were “intriguing,” more studies would be useful to better understand the effects of WASH programs.

Future results from five ongoing randomized controlled trials could help clarify the benefits of the interventions on children’s growth, Dangour said.

But Kevin McGuigan, a physicist at the Royal College of Surgeons in Dublin, Ireland, told Reuters Health that additional studies may not be money well spent.

“It’s a helpful secondary outcome as far as I’m concerned,” McGuigan said, referring to the small benefit hygiene may have on height.

The authors of the new review included three studies that McGuigan co-authored between 2010 and 2011. The review supports the findings of his 2011 Kenyan study that also found a correlation between hygiene and height.

“Height-for-age is normally taken as a good sign of a child’s overall development,” McGuigan said. “You can lose weight, but you can’t lose height.”

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SOURCE: The Cochrane Collaboration, online August 1, 2013.

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