This one is interesting. 

Did you know that in northern countries, which have dark, cold winters, couples are less likely to conceive during the winter, whereas conception rates peak in the summer?

There are a number of reasons why this association exists, but new research highlights vitamin D as one of the most important variable.

Vitamin D, a steroid hormone that influences virtually every cell in your body and has been positively linked to health conditions ranging from cancer to heart disease, may significantly boost fertility in both men and women.

So the first step to ensuring you are receiving all the benefits of vitamin D is to find out what your levels are using a 25(OH)D test, also called 25-hydroxyvitamin D.

There are two vitamin D tests -- 1,25(OH)D and 25(OH)D -- but 25(OH)D is the better marker of overall D status. It is this marker that is most strongly associated with overall health, and it is the one you should ask your physician for. The point of vitamin D testing is, of course, to be sure you are maintaining a therapeutic level of vitamin D in your blood. A few years back, the recommended level was between 40 to 60 nanograms per milliliter (ng/ml), but more recently the optimal vitamin D level has been raised to 50-70 ng/ml.

To get your levels into the healthy range, sun exposure is the BEST way to optimize your vitamin D levels; exposing a large amount of your skin until it turns the lightest shade of pink, as near to solar noon as possible, is typically necessary to achieve adequate vitamin D production. You can also take vitamins. 

Do you know your Vitamin D levels? Do you feel like you get enough sunshine?