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The immune system needs 9.5 hours of sleep in total darkness to recharge completely.
An identified risk factor for osteoporosis is the intake of excessive amounts of vitamin A. Dietary intake of approximately double the recommended daily amount of vitamin A, by women, has been shown to reduce bone mineral density and increase the chances for hip fractures compared with women who consumed the recommended daily amount (or less) of vitamin A.
Increased intake of vitamin D has been shown to reduce fractures up to 25% in older people.
The Romans did not use numerals to indicate fractions but instead used words to indicate parts of a whole.
More than 50% of American adults have oral herpes, which is commonly known as "cold sores" or "fever blisters." The herpes virus can be active on the skin surface without showing any signs or causing any symptoms.