Cow's milk and infant formula rarely contain the amount of vitamin D stated on the label and may be either underfortified or overfortified which could be hazardous to your and your child's health.

Boston University School of Medicine studied 13 brands of milk with various fat contents and five brands of infant formula purchased at random from local supermarkets in eastern United States.

The study team found that only 12 of the 42 samples taken from the brands of milk and none of the 10 samples taken from the five brands of infant formula contained a level of vitamin D between 80 to 120 per cent of the amount stated on the label. Sixty two per cent of the milk samples contained less than 80 per cent of the amount claimed; no vitamin D was detected in three of the 14 samples of skimmed milk tested. One milk sample labelled as containing vitamin D2 contained vitamin D3.

Seven of the 10 samples of infant formula contained more than 200 per cent of the amount on the label; one contained 410 per cent of the stated amount.

"Since both underfortification and overfortification are hazardous, better monitoring of the fortification process is needed," the study concluded.

In the same issue, Beth Israel Hospital in Boston reported eight cases of vitamin D intoxication caused by excessive vitamin D fortification of milk by as little as a half a cup a day. Most of them had excessive levels of calcium in the blood and one had too much calcium in the urine.

Too much vitamin D can also cause urinary stones, malfunction of the kidneys and other organs, and calcium deposits elsewhere in the body. Too little can lead to soft bones and muscle weakness.