Recommended Daily Allowance

While there is no specific recommended daily allowance for vitamin D-3 in particular, there is an RDA for vitamin D. For adults under the age of 70, the RDA of vitamin D is 600 international units. For those over the age of 70 the RDA is 800 international units. Similarly, for those over the age of 50, more vitamin D per day may be required per day to account for an increased risk of osteoporosis. To determine the correct dosage, consult a medical professional.

Sources of Vitamin D-3

Vitamin D-3 is synthesized by your body when your skin is exposed to direct sunlight. Exposure times of 15 minutes per day three times a week will be sufficient for you to synthesize enough vitamin D for your body’s needs, according to Medline Plus. However, those with darker colored skin will need longer exposure times or at greater frequency because the higher melanin content means their skin is better at blocking the UV rays needed for vitamin D-3 synthesis.

Insufficient Amounts of Vitamin D

Vitamin D-3 functions like vitamin D-2 in your body, so both forms of vitamin D are often referred to solely as vitamin D. As vitamin D is used by your body to absorb calcium, low levels of vitamin D can lead to low blood calcium levels. Without enough calcium, bone density can suffer, possibly leading to osteoporosis. Because of it’s importance in bone health and production, adequate amounts of vitamin D are particularly important for those who are going through growth periods.

Too Much Vitamin D

As a fat-soluble vitamin, excess amounts of vitamin D -- both forms of it -- are retained by your body. Too much vitamin D can cause a host of health complications, including nausea, constipation, vomiting, muscle fatigue, weight loss, disorientation and a reduced appetite. Because of its association with calcium absorption, excess vitamin D can also lead to calcium deposits forming in your soft tissue or kidney damage. The upper limit of vitamin D is 4,000 international units for adults.