What is progesterone?

Progesterone is a hormone that plays a crucial role in the menstrual cycle and in maintaining the early stages of pregnancy. It is produced after ovulation by the corpus luteum—which is the remnant of the follicle that released the egg—and is essential for life, as it opens and closes the implantation window and allows for pregnancy to occur. In the luteal phase of the menstrual cycle, the corpus luteum is stimulated to produce progesterone pulses, and if pregnancy does not occur, the corpus luteum has a limited lifespan and eventually dies, leading to a drop in estrogen and progesterone levels 1. Progesterone also has a protective effect on potential pregnancy, leading to increased sleep, increased appetite, and potentially less sexual activity, as it aims to protect against anything that could harm the baby 1. Additionally, progesterone can cross the blood-brain barrier and act as a GABA agonist, which helps with sleep and has effects similar to GABA-related medications 2.

Vitamin D's role in increasing testosterone relates to its function as a hormone and its impact on various pathways within the body. When individuals with vitamin D deficiency receive proper supplementation, their testosterone levels can be optimized. Specifically, vitamin D is a steroid hormone that binds to receptors and activates certain pathways which include the synthesis and regulation of testosterone 1.

Sunlight exposure, which enables the skin to synthesize vitamin D3, has been found to relate to increases in testosterone, with more significant effects in individuals with paler skin or those coming from regions with lower UV exposure 2. This connection is likely due to sunlight's role in vitamin D3 production, which is necessary for the appropriate functioning of various hormones, including testosterone.

Furthermore, the skin's role as an endocrine organ and its interaction with sunlight can stimulate the production and activation of hormones, including vitamin D, which then has various other downstream effects, including on testosterone levels 3.

Given that more than 5% of the protein-encoded human genome is regulated by vitamin D, deficiencies in this vitamin can impact several bodily functions, including those affecting testosterone production 4. However, it's essential to note that the relationship between vitamin D and testosterone involves a complex interplay of genetic, environmental, and metabolic factors. It's also crucial to address other underlying health issues such as inflammation that might affect vitamin D utilization before assuming benefits on testosterone levels will be realized 5.

Common sources of vitamin D include:

• Fortified foods, such as milk (both cow's milk and plant-based options like soy milk) that are often fortified with vitamin D2
• Fatty fish, which naturally contain some level of vitamin D, with cod liver oil being a notable example
• Sun exposure, which is crucial for the body's natural production of vitamin D3

It is difficult, however, to correct a vitamin D deficiency solely through diet. Adequate sun exposure, depending on the geographical location, skin type, and age, is essential since efficiency in vitamin D3 production via the skin can decline with age 1. Therefore, while certain foods and sunlight contribute to vitamin D levels, supplementation with vitamin D3 may be necessary, especially if a deficiency is present.

The daily recommended dosage of vitamin D3 can vary based on individual needs and specific circumstances. However, for many people, taking 1000 to 5000 International Units (IUs) of vitamin D3 per day is considered generally safe. Andrew Huberman has personally taken doses in this range. It's difficult to reach a point of hypercalcemia, which would be the major concern with high levels of vitamin D3 supplementation, without consuming an excessive amount far beyond normal doses. The upper tolerable intake level set by the Institute of Medicine is 4000 IUs per day, and Dr. Rhonda Patrick mentions that she takes 5000 IUs a day herself 1. It's important, however, to consult a healthcare provider before beginning supplementation to establish a dosage appropriate for individual health needs and circumstances.