Final answer:
The statement that sunscreen with an SPF of 8 or greater can inhibit vitamin D synthesis is true, as sunscreens are designed to filter out UVB rays, which are necessary for the production of vitamin D in the skin.
Step-by-step explanation:
Using a sunscreen with an SPF of 8 or greater can inhibit the synthesis of vitamin D in the skin. This statement is true. The sun protection factor (SPF) measures a sunscreen's ability to filter out UVB rays, which are the same rays that enable vitamin D synthesis in the skin. Sunscreens with an SPF value are highly effective in blocking UVB rays, with an SPF of 30 filtering about 97% of these rays according to the American Academy of Dermatology. Thus, while sunscreens protect the skin from the potential damage of UV radiation, they can also reduce the skin's ability to produce vitamin D. People, therefore, need to ensure they have adequate vitamin D intake from other sources, such as foods or nutritional supplements.