globeandmail.com: Five-point vitamin D primer:

“Dr. Cannell believes everyone should have a blood test to determine, then monitor, their vitamin D levels. He recommends going to the doctor three or four times a year and asking for a 25 Hydroxy Vitamin D level test. ”It should be between 125 and 150 nanomoles per litre,“ he said. ”It’s important that the patient not accept the doctor saying your levels are fine. They’ve got to get the number and get their levels up.“
HOLD OFF ON THE SUNSCREEN
”If you properly apply sunscreen, you might as well stay inside,“ Dr. Cannell says.”