When Cole Porter wrote, "It's delightful, it's delicious, it's de-lovely,” he had no idea how D-structive it might be to find yourself D-ficient.

But recently researchers have discovered that in the lab, at least, a high-fat diet plus insufficient vitamin D increases your risk for development of metabolic syndrome (a combination of obesity, insulin resistance and non-alcoholic fatty liver disease).

Healthy levels of the sunshine vitamin help combat it.

This matters, say the researchers, because "due to air pollution, insufficient sunlight exposure and altered dietary composition," low levels of vitamin D affect 30 to 60 percent of folks worldwide, and "is increasingly found in association with many diseases, including autoimmune diseases, hepatitis and cancer."

The most at risk? Breastfed babies, the elderly, indoor-dwellers, people with darker skin in low-light locations (north of Atlanta in the wintertime) and anyone who has trouble absorbing fat because of inflammatory bowel disease or gastric bypass surgery, for example.

D's powers seem to lie in its ability to tamp down inflammation and its positive influence over gut bacteria. So what can you do to make sure you're making smart D-cisions?

• Aim for 30 minutes of sun exposure twice a week; after that, it's mineral-based, 30-SPF sunscreen all the time!

• Get dietary D from nonfat dairy, salmon and tuna.

• Get a blood test to check your level. If you're low, consider taking at least 600 IU of vitamin D-2 or D-3 (800 IU if you're 71 or older), but no more than 4,000 IU daily.