Written by Lindsay Christensen, MS, CNS, LDN

Progesterone is often considered just a reproductive hormone necessary for menstruation, conception, and pregnancy. While progesterone is vital for these processes, the truth is that it assists with so much more than just reproduction! Progesterone is crucial for female health across the lifespan and plays a vital role in brain health, bone density, and mood regulation. Read on to learn all about progesterone, how to increase its levels naturally, and why bioidentical progesterone can be helpful in certain cases of progesterone insufficiency.

Progesterone Is Essential for Female Reproductive Health

Progesterone is a sex steroid hormone, like estrogen and testosterone. Steroid hormones are produced by the adrenal glands, gonads (ovaries and testes), and the placenta (in pregnant women). While both men and women make progesterone in their bodies, women make more progesterone and experience fluctuations in progesterone levels across their menstrual cycles. Men and women both make progesterone in their adrenal glands, but premenopausal women also make progesterone in their ovaries. In cycling women, progesterone levels peak in the second half of the menstrual cycle once ovulation has occurred and the corpus luteum is actively secreting progesterone. Progesterone levels also increase significantly during pregnancy due to placental progesterone synthesis.

In the female body, progesterone is vital for several reproduction-related processes. Progesterone is essential for conception. (1) It also assists with the maintenance of healthy periods and avoidance of premenstrual syndrome (PMS), which is believed to occur when there is relative estrogen dominance and insufficient progesterone. (2) It is also essential for maintaining pregnancy; in fact, pregnancy will fail if a woman’s progesterone levels are too low. (3)

Progesterone Modulates the Stress-Response System

Progesterone isn’t just a reproductive hormone – it is also a vital hormone mediating adaptation and resistance to stress. Research indicates that progesterone and its derivative, allopregnanolone, function to downregulate stress and anxiety and promote social engagement, which also helps the body manage stress. (4) Progesterone calms the nervous system, making the body more resilient to stress. (5) It promotes sleep (6), and sufficient sleep is an absolute necessity for a balanced stress-response system!

Progesterone Supports Gentle Aging

Later in life, progesterone serves the critical role of supporting gentle aging by protecting the brain, cardiovascular system, and skeletal system. Brain levels of progesterone strongly decrease with age; the decline in brain progesterone may play a role in age-associated cognitive decline. (7)

Progesterone is a “neurosteroid,” meaning it is a hormone that impacts the brain. While steroid hormones are primarily produced by the adrenal glands, gonads, and placenta, some research indicates that certain steroid hormones can either be synthesized in the brain or have local actions in the brain; progesterone is one of these crucial neurosteroids. (8, 9) Its small size allows it to easily cross the tightly-regulated blood-brain barrier through diffusion or transmembrane transport. (10) It can also be synthesized by glia and neurons in the brain.

Progesterone has a wide range of effects on the brain. It supports the myelination of neurons, ensuring that the fatty sheath around neurons that facilitates neurotransmission remains intact. It also protects the brain from trauma-induced damage. Progesterone influences brain function by binding to specific receptors, including intracellular progesterone receptors (PRs). It is also converted into 3α,5α-THPROG, or allopregnanolone, promoting calming GABA neurotransmission. (11)

Progesterone also supports healthy bones by supporting osteoblasts, the bone-building cells of the body that create new bone tissue. (12) Maintaining healthy, age-appropriate progesterone levels is thus crucial as women age for maintaining bone density. Progesterone is also a vasoactive hormone that can support cardiovascular health by maintaining healthy blood pressure. (13)

Progesterone Benefits the Brain and Muscle and Regulates Inflammation

Last but not least, progesterone also helps manage healthy inflammation  (14), particularly inflammation in the brain, and builds muscle. (15, 16) It really is a multi-purpose sex steroid hormone!

Symptoms and Causes of Low Progesterone

Symptoms of low progesterone include:

• Low body temperatures in the luteal phase of the menstrual cycle (if you are a cycling woman and track your body temperatures). Progesterone sufficiency stems from a well-functioning metabolism, which can be assessed through basal body temperature measurements.
• Spotting in the luteal phase of the menstrual cycle
• Dense breast tissue
• Occasional anxiousness
• Sleeplessness
• Irritability
• Heavy or irregular menstrual cycles

In premenopausal women, most progesterone comes from the corpus luteum, which forms at ovulation. Ovulation is thus a prerequisite for healthy progesterone levels in young, cycling women. Many women benefit from tracking their cycles to learn if and when they ovulate. Tools such as Natural Cycles and Temp Drop can track menstrual cycles and ovulation. Chronic stress, over-exercising, under-eating, and micronutrient deficiencies can inhibit ovulation in cycling women, lowering progesterone production.(17, 18, 19) Importantly, you don’t need to be an athlete to over-exercise; female exercise enthusiasts of all skill levels can inadvertently lower their progesterone levels by over-exercising, due to the stress that high activity levels place on the body.

In cycling women, a relative excess of estrogen can also contribute to symptoms of low progesterone. Excess estrogen may come from excess body fat or exposure to environmental xenoestrogens, such as phthalates, which can promote estrogen dominance and relative progesterone deficiency. (20, 21)

By a woman’s late 30s, her body’s production of progesterone naturally declines. The perimenopausal and postmenopausal years are associated with even greater reductions in progesterone synthesis. By the time a woman is menopausal, her adrenal glands have taken over as the primary synthesizers of progesterone, albeit secreting progesterone in levels much lower than what her ovaries formerly made. Women who enter perimenopause with HPA axis dysfunction (aka “adrenal fatigue”) are thus more likely to experience symptoms of low progesterone during this hormonal transition. Chronic stress during perimenopause will further deplete progesterone levels by causing the body to shift its resources towards cortisol production rather than progesterone production. (22)

How to Naturally Boost Progesterone Levels

There are a few ways to boost progesterone naturally, including optimizing diet and lifestyle and bioidentical progesterone replenishment.

Diet and lifestyle significantly impact progesterone synthesis in the female body. In cycling women, diet and lifestyle strategies that support ovulation facilitate healthy progesterone levels. First and foremost, the body needs an adequate energy supply (i.e., calories from food) for ovulation to occur. Research shows that caloric restriction inhibits reproductive function, chief among those effects being suppression of ovulation. (23) Therefore, young women suffering from low progesterone levels should start by making sure they’re eating enough! Certain micronutrients are also needed to promote corpus luteum development and subsequent progesterone secretion, including vitamin A, vitamin E, and vitamin D. (24, 25, 26).

Cycling women and perimenopausal women can optimize their progesterone levels by managing stress, getting 7-9 hours of high-quality sleep every night, and eating a nutrient-dense diet that supports the ovaries and adrenal glands.

Once dietary and lifestyle factors are optimized, some women may still require additional support for improving their progesterone levels. These women may benefit from bioidentical progesterone replacement. Bioidentical progesterone is a form of progesterone identical on the molecular level to the progesterone made within our bodies. Bioidentical progesterone applied topically may support healthy progesterone levels, alleviating common progesterone deficiency symptoms such as vasomotor symptoms (hot flashes), heart palpitations, mood, and sleep issues in perimenopausal women and heavy, painful periods in premenopausal women.  (27)

Progesterone is far from being just a “pregnancy hormone.” It impacts a diverse range of physiological processes in the female body, ranging from fertility to stress resilience. Insufficient progesterone levels can cause uncomfortable symptoms in the premenopausal and perimenopausal years. Fortunately, diet and lifestyle changes and bioidentical progesterone can replenish levels of this vital hormone, restoring a harmonious balance to the female body.