Final answer:
Vitamin A is the second most common micronutrient deficiency in the world, following iron deficiency. It is essential for immune function and vision, and its lack can cause serious health issues.
Step-by-step explanation:
The second most common micronutrient deficiency in the world is vitamin A. Iron deficiency is the most common, affecting approximately 2 billion people globally. Vitamin A is crucial for the immune system and vision, and its deficiency can lead to a range of problems including anaemia, increased susceptibility to infections, and various degrees of visual impairments. Iodine and zinc deficiencies are also public health concerns, but vitamin A deficiency remains more prevalent after iron.