Low dietary intake, limited sun exposure, and poor vitamin D absorption can result in vitamin D deficiency. In children, this eventually results in rickets, which is characterized by soft bones, skeletal deformities, failure to thrive, developmental delay, and dental abnormalities. In adults, vitamin D deficiency can lead to osteomalacia, which results in weak bones due to defective bone mineralization during the remodelling process. The symptoms of osteomalacia are similar to rickets.
Vitamin D deficiency is also associated with an increased risk of insulin resistance, high blood glucose, diabetes, and metabolic syndrome. This can also contribute to complications that affect the cardiovascular system, increased obesity risk, and hypertension. There is also an inverse relationship between vitamin D levels and inflammation, as lower vitamin D levels are often observed in individuals suffering from inflammatory diseases.
Vitamin D toxicity is very rare. It is usually caused by taking heavy doses of vitamin D due to misuse supplements or incorrect prescriptions. Symptoms are often nonspecific and subtle, such as weakness, fatigue, and bone pains, but can also include neurological symptoms (e.g. confusion, irritability, and comma in severe cases), gastrointestinal symptoms (e.g. abdominal pain, nausea, vomiting), renal complications (e.g. kidney stones), and heart issues (e.g. cardiac arrhythmias).