Vitamin D2 and vitamin D3 are the forms of vitamin D most important to human health, according to the Mayo Clinic. Vitamin D2 is manufactured by plants, while vitamin D3 is manufactured in the skin when it's exposed to the sun.
Population in families living in Washtenaw County ; Total Population: 238,069; Population Under 18 years: 70,878; Population 18 years and over: 167,191
According to the U.S. Census Bureau, the county has a total area of 1,695 square miles (4,390 km2), of which 572 square miles (1,480 km2) is land and 1,123 square miles (2,910 km2) (66%) is water. Alpena County is in the northeast of the mitten-shaped Lower Peninsula of Michigan.