Final answer:
Transitioning to a calcium-deficient diet leads to reduced calcium absorption due to less activated vitamin D, skeletal calcium store depletion, and increased risk of osteoporosis due to weakened bones.
Step-by-step explanation:
Effects of Calcium Deficiency in Adults
When an adult transitions from a calcium-enriched diet to a calcium-deficient diet, several events can occur as part of the body's response to maintain calcium homeostasis. Initially, a reduction in dietary calcium leads to lower levels of absorbed calcium in the intestines, due to reduced activation of vitamin D. Over time, this can result in the depletion of calcium stores in the skeleton.
The body tries to compensate for this deficit by increasing the activity of parathyroid hormone (PTH), which raises calcium levels by accelerating bone resorption, thereby releasing more calcium into the bloodstream. This PTH increase also stimulates the kidneys to reduce urinary excretion of calcium, at the same time enhancing the activation of vitamin D to increase intestinal absorption of calcium.
Despite these compensatory mechanisms, prolonged calcium deficiency can cause conditions such as osteopenia and eventually osteoporosis, characterized by weak and brittle bones, leading to an increased risk of fractures. Additionally, a continuous state of hypocalcemia affects muscle function, nerve transmission, and blood clotting.