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Alzheimer's disease affects only about 10% of people older than 65 years of age. Most forms of decreased mental function and dementia are caused by disuse (letting the mind get lazy).
The immune system needs 9.5 hours of sleep in total darkness to recharge completely.
Although the Roman numeral for the number 4 has always been taught to have been "IV," according to historians, the ancient Romans probably used "IIII" most of the time. This is partially backed up by the fact that early grandfather clocks displayed IIII for the number 4 instead of IV. Early clockmakers apparently thought that the IIII balanced out the VIII (used for the number 8) on the clock face and that it just looked better.
There are approximately 3 million unintended pregnancies in the United States each year.
On average, someone in the United States has a stroke about every 40 seconds. This is about 795,000 people per year.