A new study by Purdue University has shown that high humidity present in bathrooms and kitchens degrades the vitamins and health supplements stored in those rooms, even if the lids are on tight.
Lisa Mauer, a Purdue associate professor of food science, has shown that subjecting certain products, such as vitamin C, to humidity can chemically change their compositions, eliminating the health benefits associated with those products.
She said that crystalline substances - including vitamin C, some vitamin B forms and other dietary supplements - are prone to a process called deliquescence, in which humidity causes a water-soluble solid to dissolve.
Keeping those supplements away from warm, humid environments can help ensure their effectiveness.
"You might see salt or sugar start to cake in the summer, start to form clumps, and that's a sign of deliquescence. You can also get chemical instabilities, which are a little more problematic if you're consuming a dietary supplement with vitamin C for that vitamin C content," said Mauer.
Mauer said that kitchen salt, sugar and powdered drink mixes commonly cake, making their measurement more difficult but not rendering them useless. However, chemical changes become more than a nuisance in vitamins and dietary supplements.
"If you get some moisture present or ingredients dissolve, they'll decrease the quality and shelf life of the product and decrease the nutrient delivery," Mauer said.
"You can get complete loss of the ingredients. It depends on the conditions. It depends on the formulations. Within a very short time - in a week - you can get complete loss of vitamin C in some products that have deliquesced."
Bathrooms and kitchens can increase the detrimental effects because of spikes in humidity in those rooms. And Mauer said storing vitamins or supplements in containers with lids doesn't always help.
"Opening and closing a package will change the atmosphere in it. If you open and close a package in a bathroom, you add a little bit of humidity and moisture each time," Mauer said.
"The humidity in your kitchen or bathroom can cycle up quite high, depending on how long of a shower you take, for example, and can get higher than 98 percent," she added.
The study was published in the early online version of the Journal of Agricultural and Food Chemistry.