Final answer:
The most common cause of iron deficiency in men and postmenopausal women is chronic blood loss, often from the gastrointestinal tract, and malabsorption syndromes that prevent the adequate absorption of iron from the diet.
Step-by-step explanation:
The most frequent cause of iron deficiency in men and postmenopausal women is chronic blood loss, often due to gastro-intestinal tract disorders. In the absence of menstruation, which is the most common cause of iron loss in premenopausal women, conditions such as peptic ulcers, gastritis, colorectal cancer, or chronic aspirin ingestion can lead to significant iron loss. Malabsorption syndromes can also be a contributing factor, where iron cannot be adequately absorbed from the diet, possibly due to intestinal diseases or surgeries. To mitigate this, a diet sufficient in iron or supplementation may be advised, especially in cases where dietary intake is not meeting the body's needs.
Stores of iron are mainly maintained in the liver, spleen, and bone marrow, and any conditions that affect these can also lead to a deficiency. Furthermore, increased demands for iron such as during rapid growth, pregnancy, or lactation can exacerbate the likelihood of developing an iron deficiency if the diet does not compensate for the increased need.