was sind östrogen — what are common causes?

The provided context does not contain specific information about estrogen or its common causes. Estrogens are a group of sex hormones primarily produced in the ovaries, with smaller amounts from adrenal glands and adipose tissue. Common causes of altered estrogen levels include natural life stages (puberty, menstrual cycle, pregnancy, menopause), hormonal contraceptives, certain conditions (e.g., polycystic ovary syndrome, thyroid disorders), obesity, stress, and environmental chemicals with hormonal activity (xenoestrogens). The evidence for these associations is generally well-established in medical literature, but since the given context lacks relevant data, the evidence rating here is 'unclear'. For personal health concerns, consultation with a healthcare provider is recommended.