Speaking at the Experimental Biology meeting in San Diego, the researchers said that elderly patients who consumed 5000 IU of vitamin D and 320 mg calcium carbonate a day through a specially formulated bread had a 28 per cent increase in lumbar bone mineral density after one year.
This compares to the 8 per cent increase in bone mass density typically achieved with bone-building drugs.
Paul Stitt, founder of Natural Ovens, the US-based firm that supplied the bread and funding for the study, told NutraIngredients.com that the results confirmed the benefits of high doses of this vitamin, as well as its safety.
"We designed the study two years ago and could not get approval for use of this much vitamin D," he said.
The European Union's Scientific Committee on Food recommends an upper safe level of 50mcg (2,000 IU) vitamin D, the same level recommended by the US Food and Nutrition Board.
It is thought that higher doses of vitamin D can increase calcium levels circulating in the blood, causing the potentially serious condition, hypercalcaemia.
The new study, carried out by Dr Veronica Mocanu and colleagues at the University of Medicine in Isai, Romania, and Dr Reinhold Veith at the University of Toronto, tested for calcium excretion and found that it did not rise above 'normal values'.
"We are looking for sites where we can repeat the study and confirm our results," added Stitt.
The findings will add fuel to the debate raging over the role of vitamin D in health. Vitamin D is naturally produced by the skin's exposure to UV rays in sunlight. Studies increasingly link higher risk of certain health conditions in countries with little sunshine for long periods of the year to a vitamin D deficiency.
The bread was tested on 45 elderly nursing home patients in Romania, a location chosen because it is at a northern latitude similar to many cities where solar ultraviolet radiation intensity is low, especially in winter months.
Previous research has found that vitamin D supplementation reduces the risk of potentially life-threatening falls among institutionalised elderly people by more than 20 per cent.
Natural Ovens currently markets whole grain bread with 600 international units of natural vitamin D per slice.