Answer :The recommended intake of vitamin D-but not the safe limit-does increase with age: The Institute of Medicine has set the daily adequate intake for adults ages 19 to 50 at 200 IU of vitamin D, for ages 51 to 70 at 400 IU, and for those older than age 70 at 600 IU. Many experts, however, argue that those levels should be raised, and research has shown that 800 to 1,000 IU daily may be needed to obtain the full range of health benefits.
It is possible to get too much of a good thing, though: Vitamin D can be toxic at high levels of intake. Too much vitamin D can cause dangerous calcium deposits in organs, including the heart, and can damage the kidneys. The Institute of Medicines Tolerable Upper Intake Level (UL) for vitamin D is set at 2,000 IU daily for adults, regardless of age, although the lowest dose at which adverse effects have been registered is 3,800 IU. Given the modest amounts even in foods richest in vitamin D-98 IU in a cup of fortified milk, for example, and 360 IU in 3.5 ounces of cooked salmon-its highly unlikely you could ever eat your way to an overdose. Typical vitamin D supplements contain 400 to 800 IU in a single capsule, however, so take them judiciously.
The issue of vitamin D in fish oil actually more concerns cod liver oil, which mothers used to give their children to combat rickets (caused by a deficiency of vitamin D). A tablespoon of cod liver oil contains 1,360 IU, so its true that combining cod liver oil and vitamin D capsules could quickly exceed safe limits. Checking with two leading supplement manufacturers, however, confirms that fish-oil capsules contain levels of vitamin D too low to detect.