Scurvy on a diet devoid or nearly devoid of vitamin C, had blood levels of vitamin C too low to be accurately measured when they developed signs of scurvy, and in the Iowa study, at this time were estimated (by labeled vitamin C dilution) to have a body pool of less than 300 mg, with daily turnover of only 2.5 mg/day. The vast majority of animals and plants are able to synthesize vitamin C, through a sequence of enzyme-driven steps, which convert monosaccharides to vitamin C. However, some mammals have lost the ability to synthesize vitamin C, notably simians and tarsiers.
Vitamin D deficiency D levels falling within this normal range prevent clinical manifestations of vitamin D insufficiency as well as vitamin D toxicity from taking in too much vitamin D. Vitamin D deficiency can be asymptomatic, but may also cause several problems including: Vitamin D deficiencies are often caused by decreased exposure of the skin to sunlight. People with a darker pigment of skin or increased amounts of melanin in their skin may have decreased production of Vitamin D. Melanin absorbs ultraviolet B radiation from the sun and reduces vitamin D production. Sunscreen can also reduce vitamin D production. Medications may speed up