Final answer:
Older adults, pregnant or breastfeeding women, and premenopausal women are most at risk of low vitamin D concentrations. Vitamin D is critical for bone health, and its deficiency can lead to fragile bones. Sunlight exposure, certain foods, and supplements are necessary for maintaining adequate vitamin D levels.
Step-by-step explanation:
According to the current 2005 dietary guidelines for Americans, individuals who are most at risk of low vitamin D concentrations include older adults, women who are pregnant or breastfeeding, and premenopausal women who may need extra calcium and iron. Vitamin D is vital for bone health as it helps in the absorption of calcium, and a deficiency can lead to fragile bones and increase the risk of bone fractures. As vitamin D is not naturally abundant in many foods, it is often obtained through sunlight exposure or fortified foods. People with darker skin or those living in northern latitudes may require additional vitamin D supplementation to maintain adequate levels.
Liver plays a significant role in the synthesis of vitamin D as it converts vitamin D to 25(OH)D (calcidiol), the primary circulating form. Dietary sources of vitamin D include cod liver oil, fish liver oil, egg yolk, and fortified milk or cereal. Additionally, the action of sunlight on the skin is a key factor in endogenous vitamin D production, with different skin pigments affecting synthesis efficiency.