vitamin D

the sunshine vitamin.
Did you know it is actually a hormone produced naturally by our bodies. When we are exposed to UVB rays,  our skin produced vitamin D3 and we only produce as much as we need. It only takes about 10 minutes of unprotected exposure to UVB rays to get all the vitamin D that we need.  That being said, I think our hands and faces should always have sunscreen on them because they are typically always exposed to the sun. But maybe consider waiting 10 minutes after going outside before putting sunscreen on your arms. (Make sure you talk with your doctor/demetologist before going out without sunscreen)
Unfortunatly... here in Canada about 6-8 months out of the year, you could go outside without sunscreen all day and your body wouldnt produce any vitamin D.
This is because the sun is at the wrong angle, and the UVB rays are not strong enough to activate the vitamin D synthesis process (this DOESNT mean they arent strong enough to do damage. a sun burn in the winter is as dangerous as a sunburn in the summer).
That is why so many doctors recommend taking a vitamin D supplement.
Currently, the recommended daily intake of vitmin D is 1000 IU but a lot of research is suggesting that the number be increase to as high as 5000 - 10 000 IU.  (check out an interesting article here)

Vitamin D plays an important role in bone density. it raises blood calcium levels by increasing the absorbtion of calcium from the gut, and reabsorption of calcium from the kidneys. When blood calcium levels rise, more is stored in the bones increasing their density and strenght.
It has also been implicated in the prevention of many types of cancer, and Multiple sclerosis.  MS is almost not exisitant in equatorial regions where sunlight and vitamin D levels are typically adequate.
Vitamin D can help improve mood by alleviating Seasonal Affective Disorder (SAD/Winter blues), and can also help reduce muscle fatigue and chronic pain.
Some preliminary studies also suggest that low Vitamin D may also be linked to an increased risk in heart disease and stroke (see a brief overview of Vitamin D here)

Vitamin D is found in some foods, such as salmon, and milk and breakfast cereals are typically fortified with vitamin D (fortified means it has been added to a product that did not naturally contain that vitmain/mineral, where as enriched means vitamins and minerals that have been lost during processing have been added back in). Most multivitamins contain about 400 IU (about 10% of the body's daily need)
So how do you know if you are getting enough vitamin D?
Ask your doctor, and get your blood tested for vitamind D levels. Once the results come back talk to your doctor about how much vitamin D you should be taking every day. 1000IU may be sufficient, or they may recommend more. Make sure you follow the doctors advice because, as with all vitamins, Vitamid D does have toxic effects if taken in excess (although up to 10 000IU appears to be safe)
Write down some questions or concerns that you have before you go to the doctor so you don't forget or get overwhelmed!