I was surprised to read that vitamin pills can lose their potency in as little as seven days after they're opened, depending on the environment in which they're stored. The Daily Mail reports:
Vitamin supplements stored in a kitchen cupboard could become useless in just one week because of the humid environment, experts said yesterday.
Even keeping products in bottles with lids might not stop the pills degrading.
Food scientists found that crystalline substances - including vitamin C, some forms of vitamin B and other dietary supplements - are prone to an irreversible process called deliquescence.
It means that at levels of high humidity found in kitchens and bathrooms, essential nutrients can simply dissolve into the air.
Lisa Mauer, associate professor of food science at Purdue University, Indiana, advised storing powdered supplements in very dry areas.
Professor Mauer said: '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.
'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.'
. . .
'They're not necessarily unsafe , ' Professor Mauer added, 'but why take a vitamin if it doesn't have the vitamin content you're hoping to get?'
There's more at the link.
Thought-provoking news for me. I've usually bought the great big jars of daily multivitamin supplements sold at Wal-Mart, and kept the bottle for a year while taking one per day. However, it now appears that after a few weeks, I might not have been getting much at all out of them, if the deterioration is as marked as reported by Prof. Mauer. I think I'm going to have to change my shopping habits, buying small containers of multivitamins and using them up within a month (and storing them in less humid places, too!).