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The percent drop in the ability to make vitamin D3 in human skin with age. We normalized values to 100% using the children's values (0–20 yr). The data plotted is the average of vitamin D3 formed in the epidermis and dermis from 0–20 yr (100%), 22–40 yr (83%), 41–59 yr (66%) and 60+ yr (49%); calculated from the data in Figure 1 of MacLaughlin and Holick (1985). Note that some seniors over 70 yr make less than 25% of the vitamin D that children <21 yr can make.67
