Vitamin D is responsible for proper absorption of calcium, so you need lots of this vitamin every day for optimal bone strength. Vitamin D-3 is the form found in many supplements and most foods that are rich in vitamin D, and it's the kind your body makes when you get sun exposure. Although D-3 is beneficial, too much can lead to toxic effects.
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The majority of vitamins and minerals have a tolerable upper intake level, which is the maximum amount you can consume before experiencing dangerous side effects. For all forms of vitamin D, including D-3, adults shouldn’t have more than 4,000 international units, or 100 micrograms, in a day, according to the Food and Nutrition Board. This amount is over six times the recommended daily amount of 600 international units, or 15 micrograms.
What Can Happen
You might not even know that you took too much vitamin D, since the initial side effects are relatively general. Weight loss and urinating frequently are early warning signs. As your vitamin D level rises, it can impact your heart rhythm, leading to arrhythmia. In more severe cases, excessive vitamin D can cause your calcium level to spike, which can harden tissues and vessels. Over time, you could experience permanent artery, heart or kidney damage. These severe signs of toxicity, however, are unlikely unless you’re regularly consuming over 10,000 international units a day, reports the Office of Dietary Supplements.
Diet vs. Supplements
The tolerable upper intake level for vitamin D includes both dietary and supplemental forms. But you’re not likely to get an excessive amount of vitamin D-3, or other form of the vitamin, from your diet alone. If you take a vitamin D supplement, though, you could quickly overdose. Check your multivitamin or calcium supplement to see if it contains vitamin D before taking a separate vitamin D supplement. You might be taking more than you need.
Here Comes the Sun
Being outside for a short period -- less time than it takes for your skin to turn pink -- produces 10,000 to 25,000 international units of vitamin D-3, the Vitamin D Council reports. This is far above the tolerable upper intake level. But your system just uses what it needs, converts the leftover D-3 to an inactive form, then degrades it or stores it for later use. So even if you’re outside for an extended period of time without sunscreen or without covering up your skin, you won’t end up with toxic levels of D-3 in your body.