Final answer:
Vitamin C is essential for the immune system, assisting in the function and protection of immune cells, and those with decreased immune function require more of it to maintain their immune defense.
Step-by-step explanation:
Individuals with decreased immune function have a higher need for vitamin C because this essential nutrient plays a crucial role in supporting the immune system. Vitamin C contributes to immune defense by supporting various cellular functions of both the innate and adaptive immune system. It is known to enhance the differentiation and proliferation of B and T cells, which are vital for the immune response. Vitamin C is also an antioxidant that helps protect immune cells from oxidative stress. In cases of immunosuppression, such as in individuals with HIV, aging populations experiencing immunosenescence, or those on medications that suppress the immune system, there is an increased susceptibility to infections. This makes maintaining optimal vitamin C levels crucial. Vitamin C-rich foods include citrus fruits, fresh green vegetables, and berries. With the recommended daily requirement of about 70 mg for adults, people with compromised immune systems may benefit from higher intakes to ensure adequate support for their immune function.