Vitamin C and the common cold but it has halved the frequency of colds in people under heavy short-term physical stress. There is no effect of taking vitamin C in doses up to 8 grams per day after a cold has already begun. Vitamin C was identified in the early part of the twentieth century, and there was much interest in its possible effects on various infections including the common cold. A few controlled trials on the effect of vitamin C on the common cold were carried out already in the 1940s, the earliest of these appears to be a placebo-controlled trial published in 1945. The
Vitamin D and neurology vitamin D blood concentration standard for diagnosing hypovitaminosis D does not exist. In the past, hypovitaminosis D has been defined by blood concentrations lower than 20 ng/ mL. However, in more recent literature many researchers have considered 30 ng/ mL to be an insufficient concentration of vitamin D. Subnormal levels of vitamin D are usually caused by poor nutrition or a lack of sun exposure. Risk factors for hypovitaminosis D include premature birth, darker skin pigmentation, obesity, malabsorption, and older age. The brain requires the use of many neurosteroids to develop and function properly. These molecules are often identified as