Scurvy observed in any organism apart from humans and had been considered an exclusively human disease. Certain birds, mammals, and fish are susceptible to scurvy, but pigeons are unaffected, since they can synthesize ascorbic acid internally. Holst and Frølich found they could cure scurvy in guinea pigs with the addition of various fresh foods and extracts. This discovery of an animal experimental model for scurvy, which was made even before the essential idea of "vitamins" in foods had been put forward, has been called the single most important piece of vitamin C research. In 1915, New Zealand troops in the Gallipoli
Vitamin D deficiency increasing uptake of calcium by the kidneys and continuing to take calcium away from the bones. If prolonged, this may lead to osteoporosis in adults and rickets in children. Those most likely to be affected by vitamin D deficiency are people with little exposure to sunlight. Certain climates, dress habits, the avoidance of sun exposure and the use of too much sunscreen protection can all limit the production of vitamin D. Elderly people have a higher risk of having a vitamin D deficiency due to a combination of several risk factors, including: decreased sunlight exposure, decreased intake of vitamin D