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Human neurons are so small that they require a microscope in order to be seen. However, some neurons can be up to 3 feet long, such as those that extend from the spinal cord to the toes.
About 3% of all pregnant women will give birth to twins, which is an increase in rate of nearly 60% since the early 1980s.
Vaccines prevent between 2.5 and 4 million deaths every year.
Not getting enough sleep can greatly weaken the immune system. Lack of sleep makes you more likely to catch a cold, or more difficult to fight off an infection.
The liver is the only organ that has the ability to regenerate itself after certain types of damage. As much as 25% of the liver can be removed, and it will still regenerate back to its original shape and size. However, the liver cannot regenerate after severe damage caused by alcohol.