Understanding Vitamin D and Its Importance for Women’s Health

What Does Vitamin D Do?

Unlike most vitamins, vitamin D functions more like a hormone in the body, regulating over 200 genes, more than any other vitamin. Vitamin D is also unique because our bodies can produce it in response to sunlight. Vitamin D is a fat-soluble vitamin that exists in two primary forms: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). 

Vitamin D2 vs. Vitamin D3: Key Differences

Vitamin D2 can be found in mushrooms, especially those grown under UV light, as well as fortified foods such as cereals and plant-based milks. 

Vitamin D3 is found in animal-sourced foods, such as fish oil and egg yolks, and is also the form of vitamin D made in the skin when exposed to sunlight.

While dietary sources can contribute to our overall vitamin D levels, they typically provide smaller amounts compared to what our bodies can produce from sunlight or what we can obtain from supplements. 

Vitamin D status is measured by serum 25-hydroxyvitamin D [25(OH)D] concentrations. Higher blood levels are associated with better bone health, improved immune function, and reduced risk of chronic diseases. Research indicates that vitamin D3 (from sunlight, food, or supplements) is more effective at raising and maintaining serum 25(OH)D levels in the body compared to vitamin D2. This is because vitamin D3 binds more strongly to vitamin D receptors and stays in the bloodstream longer.

For these reasons, vitamin D3 is generally recommended as the supplement form of choice for women due to its superior efficacy in maintaining adequate vitamin D status. Understanding these differences can help you make informed decisions about how to maintain adequate vitamin D levels.

Health Benefits for Women

Vitamin D provides a wide range of health benefits that extend beyond its well-known role in supporting bone health. By ensuring adequate vitamin D levels, women can support their overall health and well-being across various aspects of life. Here are some key benefits:

Prenatal Support

Vitamin D is crucial for prenatal health and plays a vital role in supporting a healthy pregnancy, with benefits to both the mother and the baby.

Brain Function and Mood

Adequate vitamin D levels enhance brain function and play a role in mood regulation. Women with higher vitamin D levels often report better mood and lower rates of depression. Adequate vitamin D may also offer protection against cognitive decline.

Immune System Support

Vitamin D boosts immunity by enhancing the pathogen-fighting effects of monocytes and macrophages, which are critical white blood cells in immune defense. It also helps decrease inflammation.

Cardiovascular Health

Adequate vitamin D levels are associated with a lower risk of cardiovascular diseases. It helps regulate blood pressure and improve heart function.

Fertility

Low vitamin D levels can affect sexual health and fertility in both men and women. For women, adequate vitamin D levels are associated with better reproductive health.

Menstrual Health

Adequate vitamin D levels can help regulate menstrual cycles and reduce the severity of premenstrual syndrome (PMS) symptoms.

Bone Health Beyond Calcium

While vitamin D is well-known for its role in calcium absorption, it also helps maintain phosphorus levels, which are crucial for bone health.

Skin Health

Vitamin D can improve skin health by reducing inflammation and promoting skin cell growth and repair, which can be beneficial for conditions like psoriasis.

Weight Management

Some research suggests that vitamin D may play a role in weight management by influencing fat storage and metabolism.

Should I Supplement With Vitamin D?

Common signs of vitamin D deficiency include fatigue, bone pain, muscle weakness, and mood changes. Certain factors can increase the likelihood of vitamin D deficiency including limited sun exposure, darker skin, and certain medical conditions such as Crohn's disease, celiac disease, and obesity can affect vitamin D absorption and metabolism.

The most reliable way to determine your vitamin D status is through a blood test measuring 25(OH)D, which can be ordered by your healthcare provider. Levels of 50 nmol/L (20 ng/mL) or more are generally considered sufficient for most people. However, optimal serum concentrations can vary based on factors such as age, race, ethnicity, and specific health conditions and recent studies indicate that maintaining serum 25(OH)D levels above 40 ng/mL can significantly reduce the risk of various diseases.

Recommended Dosage

The recommended daily allowance (RDA) for vitamin D varies based on age, sex, and life stage. For adult women, including those who are pregnant or breastfeeding, the RDA is 600-800 IU. However, many women may benefit from, and even require, higher doses to achieve optimal vitamin D status. It's important to consult with a healthcare provider who can put all the pieces together to determine the right dosage for your individual needs.

Risks of Taking Too Much

The primary concern with high-dose vitamin D supplementation is hypercalcemia, or high levels of calcium in the blood. Fortunately, the symptoms of hypercalcemia are well known and can be resolved by discontinuing vitamin D supplementation and allowing time for levels to normalize. Signs of excessive intake can include nausea, vomiting, weakness, and, rarely, more serious complications like kidney damage. To manage these risks, it's important to have your blood levels measured before taking doses above the recommended daily allowance (RDA) and to follow the dosage recommended by your healthcare practitioner.

Conclusion

In summary, while both vitamin D2 and D3 are beneficial, vitamin D3 is the preferred form for women due to its higher potency and effectiveness in maintaining optimal vitamin D levels. Always consult with a healthcare provider to determine the best vitamin D regimen for your individual needs.

References:

1. Bilezikian JP, Formenti AM, Adler RA, et al. Vitamin D: Dosing, levels, form, and route of administration: Does one approach fit all? Rev Endocr Metab Disord. 2021;22:1201-1218.
2. Grant WB, Wimalawansa SJ, Pludowski P, Cheng RZ. Vitamin D: Evidence-Based Health Benefits and Recommendations for Population Guidelines. Nutrients. 2025;17(2):277.
3. Harvard Health. Vitamin D and your health: Breaking old rules, raising new hopes. 
4. Healthline. Vitamin D 101 — A Detailed Beginner's Guide.
5. Mayo Clinic. Vitamin D - Mayo Clinic. 
6. McCullough ML, Zoltick ES, Weinstein SJ, et al. Circulating Vitamin D and Colorectal Cancer Risk: An International Pooling Project of 17 Cohorts. J Natl Cancer Inst. 2019;111:158-169.
7. Office of Dietary Supplements. Vitamin D - Health Professional Fact Sheet. National Institutes of Health. Accessed January 22, 2025.
8. Roy NM, Al-Harthi L, Sampat N, et al. Impact of vitamin D on neurocognitive function in dementia, depression, schizophrenia and ADHD. Front Biosci. 2021;26:566-611.
9. Sex differences in vitamin D metabolism, serum levels and action. Br J Nutr. 2020.
10. Wimalawansa SJ. Physiological Basis for Using Vitamin D to Improve Health. Biomedicines. 2023;11:1542.
11. Ye H, Li Y, Liu S, et al. Association between serum 25-hydroxyvitamin D and vitamin D dietary supplementation and risk of all-cause and cardiovascular mortality among adults with hypertension. Nutr J. 2024;23(1):33.
12. Zhao W, Zhu DM, Shen Y, et al. The protective effect of vitamin D supplementation as adjunctive therapy to antidepressants on brain structural and functional connectivity of patients with major depressive disorder: A randomized controlled trial. Psychol Med. 2024;54:2403-2413.