WebMD Health News
Laura J. Martin, MD
March 4, 2010 -- The kitchen or bathroom may be the worst place in the house
to store your vitamins.
A new study shows high humidity and temperatures, such as those found in the
bathroom and kitchen, can quickly degrade the potency of vitamin C and shorten
the shelf life of vitamin supplements -- even if the bottle cap is on
Researchers found the most common types of vitamin C used in vitamin
supplements and other fortified products are prone to a process called
deliquescence, in which humidity causes a water-soluble substance to
"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," researcher Lisa Mauer, associate professor of food science
at Purdue University, says in a news release. "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%."
"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 says. "Within a very short time -- in a week -- you can get complete loss
of vitamin C in some products that have deliquesced."
Powdered vitamin C is a popular ingredient for food fortification and is one
of the most commonly added nutrients to vitamin supplements. Researchers say
because vitamin C is very unstable and its content must be declared on nutrient
labels, it is commonly used as an indication of the shelf life of foods and
For example, monitoring deterioration of vitamin C until it no longer meets
its declared label value is one way to determine a product's shelf life.
Researchers say temperature and water are the two most frequently cited
factors affecting shelf life. But information on deterioration and shelf life
of vitamin C is based on models in which temperature and relative humidity were
varied at the same time.
In contrast, this study looked at how various changes in relative humidity
and temperature, such as those found in a bathroom or kitchen, affect the
deterioration of two common forms of powdered vitamin C, ascorbic acid and
The results, published in the Journal of Agricultural and Food
Chemistry, showed relative humidity had the largest impact on vitamin C
degradation, and this effect was magnified at elevated storage
The study showed that at room temperature, sodium ascorbate and ascorbic
acid deliquesce at 86% and 98% humidity, respectively. Once the humidity or
temperature level was brought back down, the product will solidify again, but
researchers say the damage has already been done.
"Any chemical changes or degradation that have occurred before
resolidification don't reverse. You don't regain a vitamin C content after the
product resolidifies or is moved to a lower humidity," Mauer says. "The
chemical changes we've observed are not reversible."
They say keeping vitamin supplements away from warm, humid environments is
the first step to maintaining their effectiveness.
The first signs of nutrient degradation are usually brown spots, especially
on children's vitamins. Maurer recommends discarding any vitamin supplement
that is showing signs of moisture in the container or browning.
"They're not necessarily unsafe, but why give a vitamin to a kid if it
doesn't have the vitamin content you're hoping to give them?" Mauer says.
"You're just giving them candy at that point with a high sugar content."
SOURCES:Hiatt, A. Journal of Agricultural and Food Chemistry, March 2, 2010
advance online edition.News release, Purdue University.
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