One in every 10 Auckland infants is growing up with Third World-type vitamin deficiencies.

A four-year study led by paediatrician Cameron Grant, of the Starship children's hospital, has found that 12 per cent of Auckland toddlers aged from six months to two years do not have enough vitamin A, a deficiency that causes blindness in more than 250,000 children in developing countries each year.

Ten per cent of the Auckland infants - despite living in a country with bountiful sun and outdoor space - do not get enough vitamin D, a substance the body makes when it is exposed to sunlight. The study also found a quarter of Auckland infants have too little iron in their blood.

The study shows that many New Zealanders either do not know what is good for them and their children to eat, or cannot afford to buy the foods they need.

'We suspect that if we are finding these micronutrient deficiencies in a proportion of children, it implies that there are probably other micronutrients that are also deficient, and we suspect they may be having adverse effects on children's health," said Dr Grant.

Vitamin A deficiency was not common in developed countries, but it was a problem in the developing world and because some of New Zealand's infectious diseases epidemiology mirrored that, the doctors decided to study vitamins also.

Dr Grant also leads a study on Auckland's rate of childhood pneumonia, which is five to 10 times higher than in the United States. The high rate of such diseases was due partly to increasingly overcrowded houses in the past 10 to 15 years, and variable access to family doctors, he said. But it now seemed that illness also stemmed partly from poor diet.

Vitamin A, which is made in the body mainly from red fruits and vegetables such as peaches and carrots, is crucial for seeing at night. It also helps to protect the body against infectious diseases.

"If a child is admitted to hospital with measles, we give them a treatment of vitamin A," he said.

Humans need only a tiny amount of iron in the diet, around a hundredth of a gram a day. Yet it is essential to make the haemoglobin molecules in blood that carry oxygen around the body and give people strength and energy.

Dr Grant said the 24 per cent rate of iron deficiency in his study was similar to studies in the US 30 years ago where deficiency is now about 10 per cent with iron supplements common in food and for pregnant women and babies.

Here only infant formula was fortified.

"In the US, you can pick up some cereals with a magnet," Dr Grant said.

Finally, vitamin D, the "sunlight vitamin", helps the body to absorb calcium and other minerals to build bones. Children who get too little of it develop rickets, with soft bones, bow legs, a curved spine and poor teeth.