That's because your body can only absorb calcium, the primary component of bone, when vitamin D is present.

Vitamin D - Health Professional Fact Sheet Vitamin D - Health Professional Fact Sheet

Some observational studies show associations between low serum levels of 25(OH)D and increased risks of cancer incidence and death. Nico Robin witnessed Saul laughing and smiling as he was frozen apparently to death, though he survived in the end.

If you’re concerned about mercury consumption, talk with a doctor about the appropriate amount of tuna to eat weekly ( 16). However, more studies are needed to determine the benefits of vitamin D supplementation for cognitive health. The fortification of milk (a good source of calcium) and other staples, such as breakfast cereals and margarine, with vitamin D beginning in the 1930s along with the use of cod liver oil made rickets rare in the United States [ 28, 50]. Many genes encoding proteins that regulate cell proliferation, differentiation, and apoptosis are modulated in part by vitamin D.

D - definition of D by The Free Dictionary

For example, an 18-month-old child who was given 50,000 IU of vitamin D3 for 3 months experienced diarrhea, stomach pain, and other symptoms. However, it also reduces the body’s ability to make vitamin D3 from the skin, which can make you prone to deficiency ( 42). This can cause low blood vitamin D levels, especially during winter months when there is even less sunlight.Traditionally, vitamin D deficiency has been associated with rickets, a disease in which the bone tissue doesn't properly mineralize, leading to soft bones and skeletal deformities. You can find vitamin D in mushrooms, egg yolks, fatty fish, and vitamin D-fortified products, including soy milk and cereals. However, most evidence indicates that vitamin D 3 increases serum 25(OH)D levels to a greater extent and maintains these higher levels longer than vitamin D 2, even though both forms are well absorbed in the gut [ 33-36]. Experts recommend that people with typical vitamin D levels do not exceed 4,000 IU of vitamin D per day ( 24).