How do you calculate a Vitamin D3 dose?

The daily recommended dose of vitamin D for males and females ages 1 to 70 is 600 international units a day, according to WebMD. For individuals age 71 and over, the dose is 800 international units per day. Calcium should always be taken with vitamin D.

Because the body needs vitamin D in order to absorb calcium, calcium should be taken with vitamin D in doses of 700 to 1,200 milligrams per day, depending upon age and gender, WebMD recommends. Individuals with insufficient amounts of calcium and vitamin D throughout life are at risk for osteoporosis in later years. Children who don't get enough vitamin D may not grow as much as others their age and are at risk for a rare disease called rickets, which causes weak bones.

The best vitamin D foods are salmon, tuna and mackerel, notes WebMD. Vitamin D is found in fortified foods such as milk, cereal, orange juice, yogurt, margarine and soy drinks. Individuals who do not get enough calcium and vitamin D in their diet may need supplements. Vitamin D supplements are available as ergocalciferol, known as D-2, and cholecalciferol, known as D-3. Spreading calcium out over the course of the day and taking 500 milligrams at a time reduces stomach upset and promotes better absorption.