Vitamins may not be giving you the health-giving qualities you think - and it's all down to how, and where, you store them in your home. Most people store their vitamins in cupboards in bathrooms and kitchens, and that's the very worst place to keep them, says a researcher at Purdue University in West Lafayette, Indiana. Vitamin C can lose its effectiveness within a week of being stored in humid conditions, even if the bottle lids are screwed on tight. The vitamin, along with the B vitamins and other dietary supplements, quickly dissolve in the high humidity of a kitchen or bathroom in a process called deliquescence, says Prof Lisa Mauer. The same goes for children's vitamins; after a short time stored in one of the rooms, they become nothing more than "candy with a high sugar content," she says. (Source: Journal of Agricultural and Food Chemistry, February 17, 2010: doi: 10.1021/jf903342f).