Which of the following is a characteristic of vitamin d nutrition? a. pigments in dark skins increase vitamin d synthesis. b. only about one-half of the world's population relies on sunlight to maintain adequate vitamin d nutrition c. prolonged exposure to sunlight degrades the vitamin d precursor in skin, thus preventing vitamin d toxicity d. vitamin d deficiency may be created by a calcium deficiency e. in people living in northern u. s. cities, vitamin d stores from synthesis during the summer are usually sufficient to meet the needs during the winter

b. Only about one-half of the world's population relies on sunlight to maintain adequate vitamin D nutrition  

Explanation:

Dark skin pigments slow down the synthesis of vitamin D, so black people need to spend more time in the sun to absorb enough vitamin D, so the letter A is incorrect.

Prolonged exposure to sunlight degrades the precursor of vitamin D, whereas prolonged exposure to sunlight produces vitamin D3, which acts to regulate heart function and blood pressure.  With this we can conclude that the letter C is also incorrect.

Vitamin D deficiency is not caused by calcium deficiency, on the contrary, vitamin D deficiency is a cause of calcium deficiency. In addition, summer vitamin D synthesis stocks are usually not sufficient to meet summer vitamin D requirements. That is why the letter D is also incorrect.

We can conclude, then, that the correct answer is the letter B. The main source of vitamin production is through sun exposure, because type B ultraviolet rays (UVB) are able to activate the synthesis of this substance. Some foods, especially fatty fish, are sources of vitamin D, but the sun is responsible for 80 to 90% of the vitamin the body receives. It can also be produced in the laboratory and given as a supplement when there is a deficiency and for the prevention and treatment of a variety of diseases.