Giving breastfeeding mothers monthly high-dose vitamin D supplements could be a way of helping their babies' get sufficient amounts of the vitamin, Otago University research suggests.
Vitamin D, essential for calcium and bone metabolism, is obtained mainly from exposure to sunlight, and only low levels are found in food and breast milk.
Being exclusively breastfed is a risk factor for infant deficiency of the vitamin, which can lead to the bone disorder rickets.
Study co-author Dr Ben Wheeler says there is growing concern internationally that the number of children suffering from vitamin D deficiency is increasing.
He says many countries recommend giving babies daily vitamin D supplements during breastfeeding, but this advice was often not followed.
"We wanted to see if having mothers take a monthly, high-dose supplement could offer another way to help infants get sufficient levels of the vitamin," he said.
The study involved a trial in which 90 new mothers who intended to breastfeed exclusively for six months were given different doses of vitamin D supplements for four months.
The doses ranged from 0mg (placebo group) to 2.5mg.
The researchers found that for the women given the highest dose, their babies had notably higher blood vitamin D levels 16 weeks later, compared with the placebo group.
Dr Wheeler said that, at that dose, the improvement in vitamin D status appeared to offer some protection against moderate to severe deficiency in infants.
If further research confirmed the study's findings, he said the next step would be to investigate how monthly supplements compared in effectiveness with weekly or daily doses.
The study's findings have been published in the American Nutrition Society's The Journal of Nutrition.