Nutrient deficiency occurs when the body does not receive enough essential vitamins and minerals needed for proper functioning. This can result from inadequate dietary intake, poor absorption, or increased nutritional needs due to factors like illness or pregnancy. Common deficiencies include iron, vitamin D, and vitamin B12, which can lead to various health issues. Symptoms of nutrient deficiency vary depending on the specific nutrient lacking. For example, iron deficiency can cause fatigue and weakness, while vitamin D deficiency may lead to bone pain and muscle weakness. Addressing these deficiencies often involves dietary changes or supplementation to restore balance and promote overall health.