DHAKA: Scampering up the wall of his tin shack in Bangladesh's capital, three-year-old Rozzob Ali has the same combination of mischief, charm and boisterous energy as many other boys.

But the fourth of five children, all born in a Dhaka slum, Ali shows one danger sign - at 80 centimetres tall, he is a good 10 cms shorter than the ideal height for a boy his age.

Poverty and a diet of mostly boiled rice or mashed potato are partly to blame for his stunting, which is caused by a lack of nutrients, protein, vitamins and minerals found in meat, fruit and vegetables.

Research shows that insufficient nutrition in the first 1,000 days of a child's life can lead to irreversible damage to health, growth and development.

Nutritious food has become even harder to afford since Ali's father was forced to work in a brick factory to pay off a debt.

It will take him at least six months to pay back what he owes, depriving the family of the little income he would earn pulling rickshaws around Dhaka's teeming streets.

"How can I feed the children? How can I pay the rent?" said Ali's mother, Taslima Begum, who spends her days picking up discarded plastic bottles in an upmarket neighbourhood to sell for recycling in the hope of making a dollar or two.

The rate of stunting in under-fives in Bangladesh has fallen to 36 percent from 45 percent in 2000, official figures show, partly due to a growing economy which has helped lift some 20 million people out of poverty over the last two decades.

But more than 5.5 million Bangladeshi children under the age of five are still affected by the condition.

Health experts say a major challenge for the government is to reduce stunting especially in ever-expanding slums, where it is worse than in other areas.

"There has been a reduction in the level of stunting in Bangladesh but it remains unacceptably high," Anuradha Narayan, nutrition chief at the United Nations Children's Fund (UNICEF) in Bangladesh, told the Thomson Reuters Foundation.

"At present, Bangladesh is still one of 20 countries in the world with the largest burden of stunting among children."

DISEASE, INFECTIONS

A 2016 survey by UNICEF and the Bangladeshi government shows the poorest children are disproportionately affected with 40 percent of children in slums who are stunted, compared with the overall urban average of 26 percent.

"Children in urban slums tend to be from families that are among the most vulnerable," Narayan said. "Families in urban slums might be more food insecure, but also live in environments which increase the risk of disease and infections."

Of Bangladesh's 160 million people, around 2.2 million live in 14,000 slums, according to a 2014 slum census.

In Balurmath slum where Ali grew up, the putrid smell of sewerage seeps through the air as children play barefoot in the narrow alleys lined by corrugated iron houses.

Residents bathe in the open, close to women filleting fish and girls cooking on mud stoves.

Poor sanitation and diseases linked to dirty water such as diarrhoea, which causes vital nutrients to be lost from the body, are a common scourge.

UNICEF's Narayan said progress was hampered by the government's focus on development through infrastructure.

"Investments in nutrition don't get attention that a bridge or road or infrastructure project might get," she said.

Ministry of health officials agree more needs to be done to improve nutrition among slum residents.

"We're trying to address this in a different way," Roxana Quader, a senior ministry official, told the Thomson Reuters Foundation, without giving details.

DEVELOPMENT PRIORITY

Last October, the World Bank announced it would increase funding to tackle stunting in Bangladesh to $1 billion over the next three years from about $330 million it has invested in two programmes.

Part of the money would be spent giving 600,000 families cash to buy nutritious food for their children in return for regular monitoring of their development, including height and weight.

"Investing in reducing child stunting should be a priority in Bangladesh," Qimiao Fan, the World Bank's Bangladesh country director, told the Thomson Reuters Foundation.

If Bangladesh is to achieve its target of becoming a middle-income country by 2021, "investing in child nutrition and their cognitive development is among the most cost-effective development actions," Fan said.

Health experts say this is critical because under-nourished girls tend to grow up and give birth to under-nourished babies - unless action is taken.

They say more awareness needs to be raised about the link between early marriage and stunting, and the importance of allowing more time between pregnancies to give mothers a chance to regain their health.

By the age of 27, Ali's mother had already given birth to five children. The oldest, a girl, is 12.

For many struggling to survive in the slums, nutritious food remains a luxury they cannot afford.

Manik Mia, a father of six, worries about his daughter Jannatul who turned five this month. Measuring 82 centimetres, she is severely stunted.

He spends the $38 monthly income that one of his daughters earns as a maid on paying the rent. Anything else goes on food.

"We know eggs and milk are good for babies but how can we buy them?" he said with a shrug.