From the Guidelines

Estrogen levels are highest during the luteal phase and also peak around day 12-14 of a normal menstrual cycle, just before ovulation.

The menstrual cycle is characterized by fluctuations in hormone levels, including estrogen, progesterone, follicle-stimulating hormone, and luteinising hormone 1.
Estrogen levels increase during the follicular phase, peak around day 12-14, and then rise again during the luteal phase before declining 1.
High estrogen levels during the luteal phase improve glucose metabolism, increase glucose availability, and enhance glycogen storage in skeletal muscle 1.
Estrogen also has anabolic effects, including improving muscle strength and bone mineral density, and causes a protein-sparing effect during exercise 1.
The effects of estrogen on exercise performance and metabolism are complex and influenced by various factors, including the phase of the menstrual cycle, exercise intensity, and dietary carbohydrate intake 1.

From the Research

Estrogen levels vary throughout the menstrual cycle, with significant changes in different phases 2.
The early luteal phase has been identified as the phase with the highest estrogen levels, with 80% of cases showing estrogen receptor expression 2.
In contrast, the early follicular, late follicular, and late luteal phases have lower estrogen receptor expression rates, ranging from 49% to 53% 2.

The level of estrogen at different life stages should be managed differently, as it can impact long-term health and lifespan 3.
Ovariectomy, which reduces estrogen levels, can lead to complications such as early menopause, heart disease, and osteoporosis, highlighting the importance of estrogen in women's health 3.
The metabolism of endogenous and exogenous estrogens plays a crucial role in determining therapeutic estrogen levels, with different estrogens undergoing various metabolic reactions 4.

There are four principal endogenous estrogens: estrone (E1), estradiol (E2), estriol (E3), and estetrol (E4), each with distinct metabolic pathways 4.
Exogenous estrogens, such as micronized E2 and conjugated equine estrogens, also undergo phase I and phase II reactions, resulting in different metabolites 4.
Further research is needed to understand the mechanisms of estrogen metabolism and its impact on therapeutic dosing and physiological regulation 4.