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Approximately one in three babies in the United States is now delivered by cesarean section. The number of cesarean sections in the United States has risen 46% since 1996.
The average human gut is home to perhaps 500 to 1,000 different species of bacteria.
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
There are over 65,000 known species of protozoa. About 10,000 species are parasitic.
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.