From October to March, the sun isn’t strong enough north of Los Angeles and Atlanta to prod your body into making much vitamin D-3. That endangers your immune system, makes you vulnerable to depression and overeating, weakens your bones and increases your risk for certain cancers. And then there’s the newest D-3 alert: Lack of vitamin D-3 in older adults is associated with cognitive decline and Alzheimer’s disease.

And while as far as we know there’s no chance lack of sunlight will turn you into an underground-dwelling, light-averse Morlock, those are pretty significant, but quite correctable, health risks.

What’s the solution? Even if you head to sunnier climes, or live there year-round, chances are you’re not outside enough to get the D-3 machine going (90 percent of your time is spent indoors). That’s why only a quarter to a third of Americans and Canadians have the recommended minimum blood levels of vitamin D-3. So, we suggest:

Get a vitamin D-3 blood test: If your reading comes back below 50, you need a D-boost plan. (Over 100 may be too high and trigger its own set of problems.)

Choose D-packed foods: Canned salmon dishes up 500 IU of D-3 in every 3-ounce serving. Other good sources: vitamin D-enriched low-fat milk and OJ (100 IU per glass). One study showed that women over 70 who get the most vitamin D from their food were a whopping 77 percent less likely to develop dementia.

Take a supplement: D-3 is the form you want – 1,000 IU a day; 1,200 if you’re 60 plus.

– Dr. Michael Roizen & Dr. Mehmet Oz

© 2012 Michael Roizen, M.D. and Mehmet Oz, M.D. Distributed by King Features Syndicate, Inc.