Researchers have found potentially life-saving drugs are less effective when the sun is shining because extra vitamin D produced in one’s body breaks down the drugs at a faster rate, The Daily Mail reported.

The study, based on 6,000 people, looked at 70,000 blood samples from transplant patients who were taking immune suppressing drugs over the course of a decade.

The study was done in Stockholm, Sweden, and scientists compared the samples taken during the winter months to samples taken during the summer months. In Stockholm, the winter months only have a few hours of daylight and very few sunny days.

Researchers from the Karolinska Institute are now suggesting that doctors increase certain drugs in summer months and reduce some medications in winter months. They found that the drugs were absorbed in the body depending on how much vitamin D a person had – which was dependent on how much sunlight they were exposed to.

The study is published in the journal Drug Metabolism and Disposition.

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