Caught an old rerun of an Oprah show last night. Watched just long enough to hear a very enthusiastic doctor offering advice on vitamin D. All women need to have their vitamin D levels checked, she said, because most women don't get enough. And if we're not getting enough, we need to know this so we can make necessary adjustments.

Vitamin D is critical to our health -- a deficiency can result in bone problems, cancer, high blood pressure, depression, and immune-system disorders such as multiple sclerosis, rheumatoid arthritis. and diabetes. We need about 2,000 international units of it each day, says the good doctor, not the 400 currently recommended by the FDA.

Oprah said she's had her vitamin D levels checked. They were low. No surprise. So she started taking a supplement to bump her into a better range. Supplements are good. So is the sun -- just 15 minutes per day, and don't burn. And of course, vitamin D rich foods, like wild salmon, shrimp, skim and low-fat milk, Shittake mushrooms, fortified yogurts, and fortified cereals.

Do you know your vitamin D levels? I don't. But I should.