Cole Porter's song "It's De-Lovely" is decidedly divergent with its definition of D: "It's delightful, it's delicious/It's delectable, it's delirious/It's dilemma, it's delimit/it's deluxe/It's de-lovely."

The scientific opinions on the virtues of vitamin D are almost as diverse.

On the plus side, high levels of the nutrient are associated with reduction of some cancers, improved immune function, and increased bone strength. But too much can lower blood levels of atorvastatin. And in some (but not all) studies, supplementation with D didn't reduce cardiovascular risks or help prevent falls in older adults.

It also hasn't proved effective against seasonal affective disorder, upper respiratory infections, or mild psoriasis.

Now there’s been one more study of the powers of vitamin D. And this time, it’s good news about the vitamin’s ability to help prevent loss of muscle strength.

Researchers analyzed data on around 3,200 people ages 50 and older. They found that when your body has enough vitamin D, it helps repair muscles and aids in releasing calcium for muscle contractions.

But participants who were D-ficient — with blood levels below 30 nmol/L — had 78% greater risk of muscle weakness; and those who were low but not deficient (blood levels of 30 nmol/L to 50 nmol/L) had a 77% higher risk.

Vitamin D is clearly important for many bodily functions. To get enough, eat vitamin D-fortified foods as well as salmon and mushrooms; and get a blood test to check serum levels before you take a supplement.

Until that measurement, I recommend around 1,000 IU a day of D3. After that, do what your doctor recommends.