Written by: Kelsi Irvine, R&D Scientist

Valentine’s Day, Love, and Immunity

Valentine’s Day is a celebration of love, connection, and harmony. How do these feelings affect our bodies? Well, it is different for every body. The immune system, the primary defender of our health, works differently in men and women due to biological differences like hormone levels and reproductive functions. These differences influence how our bodies fight illness, adapt to changes, and even support reproduction. In this blog, we’ll explore how sex differences shape our immune systems, and how love, immunity, and health relate to one another.

How Men and Women Experience Immunity Differently

The immune system is a finely tuned machine that utilizes many different types of cells to protect your body against health threats. There are many molecules in the body that act as signals to turn these immune cells on and off, including the major sex hormones: testosterone, estrogen, and progesterone.¹ Both men and women have all three hormones in their body, but at different levels.

Women have higher levels of estrogen and progesterone, and men have higher levels of testosterone. All three hormones play a role in activating immune cells. Testosterone has been shown to reduce immune cell activity compared to estrogen and progesterone.¹ Because men and women have different concentrations of sex hormones, their immune cells are activated at different rates.

Additionally, women’s immune systems are influenced by monthly hormonal changes during menstruation. Fluctuations in estrogen and progesterone during the menstrual cycle can alter immune function.² Pregnancy introduces even more dramatic shifts, as the immune system must adapt to support a growing fetus.³ Men, by contrast, experience fewer hormonal changes, resulting in a more stable, consistent immune response.

Because sex hormones influence the activation of immune cells, women tend to have a stronger immune response that lasts slightly longer than men’s in the face of health threats. This can help women eliminate a threat more efficiently, but their own tissue can be damaged in the process.⁴ On the other hand, men may not get over an illness as quickly, but they are less likely to damage their body’s tissue, which helps them avoid chronic inflammation and other complications. This might help explain why men often seem to experience more intense symptoms during illness, sometimes humorously referred to as a “man flu.”⁴

A review article by Sabra L. Klein, published in 2016, explores past research related to sex differences in immunity. The research suggests that men’s immune systems are less active in many ways and women’s are more active.¹ This may sound like a win for the ladies, but just as an underactive immune system can lead to health problems, an overactive immune system also has its disadvantages. Each makes men and women more susceptible to different health threats.

Women are four times more likely to develop an autoimmune disease—such as rheumatoid arthritis, multiple sclerosis, or lupus—than men.⁵ However, men are more likely to develop non-reproductive cancers and have a higher mortality rate associated with those cancers. Men also had a higher mortality rate when they contracted the flu or Covid-19.⁶ This may be in part due to their slightly less active immune system.¹

Despite having different immune strengths and weaknesses, both men and women can have healthy, functioning immune systems. By understanding these differences, both men and women can better appreciate their unique immune systems and take steps to support them.

Immune Harmony in Sex and Reproduction

The immune system’s primary job is to protect the body from threats, but when it comes to reproduction, it has to strike a delicate balance. For fertilization and pregnancy to occur, the immune system must adjust to tolerate the presence of foreign DNA from both sperm and the developing baby. This amazing connection between immunity and reproduction shows how the body works in harmony to support fertility and life.

Sexual activity alters immunity to support fertility. Pregnancy requires the immune system to tolerate foreign antibodies located on both sperm before fertilization and the embryo after. A study conducted by Tierney Lorenz in 2015 found that sexually active, non-pregnant women had a shift in immune cells that overall decrease the immune response in the uterus during the luteal phase (when the uterus prepares for pregnancy). However, women who were not sexually active did not display a shift in immune cells during their menstrual cycle.⁷ Beyond its essential role in fertilization, sexual activity also plays an important role in preparing the immune environment of the female reproductive tract for pregnancy.

Before sex and fertilization, the immune system in the male reproductive tract is already working to maintain balance in protecting reproductive organs from threats and keeping sperm healthy. Sperm health is very dependent on a man’s balanced immune system. The testes have something called “immune privilege,” which means the body sends signals for the immune system not to attack in that area. This is because immature sperm cells have antibodies the immune system recognizes as foreign.⁸ When this balance is disrupted and the immune system isn’t adequately suppressed, it can mistakenly attack sperm, leading to an autoimmune response and contributing to male infertility.⁸

Supporting Your Individual Health Along with Immune Balance

Our immune systems are a testament to the intricate design of our bodies, reflecting unique strengths and challenges shaped by our biology. By understanding how men’s and women’s immune systems differ, we can better appreciate and support our health at every stage of life. For both sexes, maintaining a healthy immune system is essential for overall well-being.

Are you looking to support your immune system while also supporting the unique needs of your body? Consider 4Life Transform® Man and 4Life Transform® Woman for male and female-focused support. Both provide immune support while also delivering specialized ingredients for men and women's health.*

Now that Valentine’s Day has passed, keep the love going by nurturing your body’s balance and harmony—consider ways to support your immune system for a healthier future!*

References:

1. Klein, S. L., & Flanagan, K. L. (2016). Sex differences in immune responses. Nature Reviews Immunology, 16(10), 626–638.
2. Oertelt-Prigione, S. (2012). Immunology and the menstrual cycle. Autoimmunity Reviews, 11(6–7), 485–490.
3. Hewings-Martin, Y. (2017, September 2). What happens to the immune system during pregnancy? Medical News Today.
4. McGettrick, H., & Iqbal, A. (2024, August 16). How biological differences between men and women alter immune responses – and affect women’s health. The Conversation.
5. Kronzer, V. L., Kodumudi, N., & Crowson, C. S. (2020). Why women have more autoimmune diseases than men: An evolutionary perspective. Evolutionary Applications, 14(3), 629–633.
6. Wilson, C. (2023). Are there sex differences in the immune system? New Scientist, 257(3424), 40.
7. Lorenz, T. K., Heiman, J. R., Demas, G. E., & Hayes, L. D. (2015). Interaction of menstrual cycle phase and sexual activity predicts mucosal and systemic humoral immunity in healthy women. Physiology & Behavior, 152, 92–98.
8. Hedger, M. P. (2015). The immunophysiology of male reproduction. Knobil and Neill’s Physiology of Reproduction, 805–892.
9. Mahajan, D., Sharma, N. R., Raghav, S. K., & Saha, S. C. (2022). Role of natural killer cells during pregnancy and related complications. Biomolecules, 12(1), 68.

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