The most common dietary deficiencies worldwide include iron, vitamin D, vitamin A, and iodine. Iron deficiency can lead to anemia, significantly impacting energy levels and cognitive function. Vitamin D deficiency affects bone health and immune function, while vitamin A is essential for vision and skin health. Iodine is crucial for proper thyroid function. Addressing these deficiencies often involves adjusting dietary practices to ensure adequate intake of essential nutrients, which is vital for maintaining overall health and preventing a wide range of health issues.