Final answer:
Low estrogen can cause disrupted menstrual function and decreased bone density when considering low energy availability.
Step-by-step explanation:
Low estrogen can cause disrupted menstrual function when considering low energy availability. When energy availability is low, females shift energy away from reproduction and toward their own survival, leading to changes in menstrual function. This can result in irregular or absent periods.
In addition, low estrogen levels can also contribute to decreased bone density and increased risk of osteoporosis. Estrogen is involved in calcium metabolism, and without it, blood levels of calcium decrease. To replenish the blood, calcium is lost from bone, leading to a decrease in bone density.