Vitamin D, also sometimes called the "sunshine vitamin," is essential for healthy bone production and growth, since it helps your body absorb more dietary calcium. Not having enough vitamin D in your system means you will absorb almost 50 percent less dietary calcium than you would otherwise. A lack of vitamin D in your system is indicated by a blood test measuring vitamin D levels, and if left untreated, a deficiency can lead to poor bone health and some diseases. Muscle problems, which can be experienced as numbness in your extremities, along with other symptoms, are an indication of having too much vitamin D in your system.
Lack of Vitamin D
Without enough vitamin D, your body will absorb only 10 percent to 15 percent of all available dietary calcium. In the presence of adequate vitamin D, you will absorb between 30 percent and 40 percent of available dietary calcium. Over time, if your vitamin D levels are not raised, you can develop poor bone health, leading to rickets or osteoporosis. Low vitamin D has also been associated with softening bones, seasonal affective disorder and a greater risk of developing high blood pressure.
Excess Vitamin D
Vitamin D is a fat-soluble vitamin that is stored in your body fat and your liver. Excess amounts of vitamin D lead to several complications, including calcium deposits in your soft tissue, kidney damage and kidney stones. Symptoms of excess vitamin D consumption include muscle problems -- which can be experienced as numbness, fatigue, bone pain, loss of appetite, weight loss, extreme thirst, vomiting, diarrhea, constipation, sore eyes and itchy skin.
Recommended Dietary Amount and Upper Limit
The recommended dietary amount of vitamin D for children and adults under 70 is 600 international units (IU). For adults over 50, sometimes the RDA is higher, but a doctor needs to decide the specific amount. For the elderly, those over the age of 70, 800 IU a day is recommended. For infants, the RDA is 400 IU. For all children and adults, the upper limits of vitamin D ingestion is 4,000 IU per day; for infants, it's 1,500 IU. Taking more than this can lead to vitamin toxicity.
Sources of Vitamin D
Vitamin D can be ingested as part of your diet or as a supplement. Vitamin D supplements contain between 50 to 1,000 international units per capsule, or around 400 international units if it is part of a multivitamin. Dietary sources of vitamin D are limited, and it is difficult to get enough vitamin D through diet alone. Fatty fish -- including tuna and salmon -- as well as dairy products and oysters are rich in vitamin D. Milk, soy products and cereals are also frequently fortified with the vitamin. Lastly, vitamin D can be synthesized by your body through direct sun exposure. Unless you have darker-colored skin, between 10 and 15 minutes of exposure three times a week will provide you with enough vitamin D. Those with darker skin tones may require more exposure time since their skin absorbs less sunlight.