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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).
After a vasectomy, it takes about 12 ejaculations to clear out sperm that were already beyond the blocked area.
Serum cholesterol testing in adults is recommended every 1 to 5 years. People with diabetes and a family history of high cholesterol should be tested even more frequently.
Vaccines cause herd immunity. If the majority of people in a community have been vaccinated against a disease, an unvaccinated person is less likely to get the disease since others are less likely to become sick from it and spread the disease.
About 3% of all pregnant women will give birth to twins, which is an increase in rate of nearly 60% since the early 1980s.