The researchers reviewed the hospital records of patients taking various immunosuppressants over the course of 10 years. Then they examined blood samples to find that concentrations of the drugs decreased by 20 percent in the summer months. This might not seem like a lot, but it’s enough for your body to notice a difference, the researchers say.
The culprit? Vitamin D. “Vitamin D stimulates an enzyme in the liver,” explains study coauthor Erik Eliasson, M.D., professor at Karolinska Institutet. “This enzyme eliminates foreign substances from the body, meaning you flush out the drug faster.”
Many types of drugs may be impacted: “We chose immune system suppressing drugs because we knew the same individuals would be taking them for long periods of time,” explains Dr. Eliasson. “But the findings could also apply to other drugs, including antidepressants and painkillers.”
Obligatory (and hopefully, obvious) warning: “This doesn’t mean you should increase your dosage over the summer without consulting a doctor,” says Dr. Eliasson. But be on the lookout for side effects as the summer approaches. If you notice that your symptoms are worse, speak with your doc about upping the dose or switching meds.