A light menstrual cycle can be caused by estrogen levels gaining balance, estrogen levels decreasing near menopause, an ectopic pregnancy, birth control hormones, eating disorders, stress, excessive exercising or low body weight, according to Everyday Health. It may also indicate thyroid or other gland problems or polycystic ovary syndrome. Light menstrual cycles also occur naturally with no underlying health issues.
The thickness of the endometrium determines the bleeding that happens during each period, according to Everyday Health. Estrogen creates the endometrium. Younger women have an irregular amount of estrogen, and estrogen levels decrease as older women reach menopause.
If a light menstrual cycle suddenly occurs, Everyday Health advises medical consultation. An accurate journal kept to be shared with a doctor is the most effective way to determine if a light menstrual cycle is natural or is a symptom of a condition such as a thyroid dysfunction, pituitary gland and hypothalamus issue or polycystic ovary syndrome.
Birth control methods such as the hormonal intrauterine device decreases the menstrual flow level by suppressing uterine lining growth, which is an expected and healthy symptom, according to Everyday Health.
Three to seven days of bleeding is normal, according to Everyday Health, and a full cycle can last from 21 to 35 days. What is considered a normal and light menstruation varies with each woman. A cycle that is always light or becomes light on a pattern may not be considered abnormal.