What is a common consequence of insufficient vitamin D levels?

Insufficient vitamin D levels lead to poor calcium absorption, which is critical for maintaining bone health and overall physiological functions. Vitamin D plays a vital role in the body's ability to absorb calcium from the digestive tract; without adequate vitamin D, the intestines cannot absorb sufficient calcium, which can result in weakened bones and an increased risk of osteoporosis. This deficiency can also lead to muscle weakness, as calcium is essential for muscle contractions.

In contrast, improved immune function, enhanced energy levels, and increased muscle strength are typically associated with adequate levels of vitamin D rather than a consequence of its deficiency. Therefore, poor calcium absorption is the most directly impacted consequence of insufficient vitamin D levels.