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Giardia is one of the most common intestinal parasites worldwide, and infects up to 20% of the world population, mostly in poorer countries with inadequate sanitation. Infections are most common in children, though chronic Giardia is more common in adults.
The average adult has about 21 square feet of skin.
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.
Sperm cells are so tiny that 400 to 500 million (400,000,000–500,000,000) of them fit onto 1 tsp.
Illicit drug use costs the United States approximately $181 billion every year.