This can cause a number of health problems including soft bones (rickets), increased asthma symptoms, cancer, increase in weight gain later in life, cognitive problems in older adults, depression, fatique, and muscle weakness. You may want to increase your vitamin D consumption before these problems develop.
One study even found that people with a vitamin D deficiency when they were diagnosed with breast cancer had a 94% greater chance of the cancer spreading. Scary. In addition, they had a 74% greater chance of dying over the next 10 years. http://www.webmd.com/food-recipes/slideshow-vitamin-d-overview
Vitamin D is added to some dairy and other products and is found naturally in fish, fish liver oils, and egg yolks. We can also get it in winter by getting a vitamin D lamp that can help our body generate the vitamin D it needs. Or you can always head south, below the latitude of Los Angeles, in winter to get your vitamin D. Your body can store extra in your fat cells for a short period.
If you currently have a deficiency, you may need more vitamin D to help restore your body to normal, but the recommendations from the Institute of Medicine are:
"Guidelines from the Institute of Medicine call for increasing the recommended dietary allowance (RDA) of vitamin D to 600 international units (IU) for everyone aged 1-70, and raising it to 800 IU for adults older than 70 to optimize bone health."
How do you know if your vitamin D levels are low? A simple blood test from your doctor will tell you. There are at home tests you can order over the internet if you prefer that option.
Not getting enough sunlight or enough food sources of milk are the most common reasons people are deficient. Some other reasons for a vitamin D deficiency might be: you have dark skin. (This reduces body's ability to synthesize vitamin D), your kidneys as they age have a harder time converting vitamin D to a form you can use, your digestive tract cannot absorb enough vitamin D for you, or you are seriously overweight.
Here is a link with an interesting slideshow from WebMD about Vitamin D.
I hope this helps! Get healthier this week!