Low Libido: Blood Tests That May Reveal Why

A disappearing sex drive is one of the most common concerns women bring up - and one of the most quickly dismissed. "It's just stress" or "that's normal at your age" are responses many women hear. But low libido almost always has identifiable contributing factors, and lab testing can help uncover them.

Why Libido Drops

Sexual desire is regulated by a complex interplay of hormones, neurotransmitters, and overall health. When any of these systems are disrupted, libido often suffers.

Research published in the *Journal of Sexual Medicine* found that up to 40% of women report sexual concerns, with low desire being the most common complaint (Shifren et al., 2008). And while psychological factors matter, physical causes are frequently overlooked.

Hormonal Causes

Low Testosterone

Testosterone isn't just a "male hormone." Women produce it too, and it plays a critical role in sexual desire, arousal, and satisfaction. A study in the *New England Journal of Medicine* demonstrated that testosterone therapy significantly improved sexual function in postmenopausal women with low desire (Davis et al., 2008).

What to test: - Total Testosterone - Free Testosterone - SHBG (Sex Hormone Binding Globulin)

Why SHBG matters: SHBG binds to testosterone, making it unavailable. Oral contraceptives can increase SHBG by 200-400%, dramatically reducing free testosterone (Zimmerman et al., 2014). This effect can persist even after stopping the pill.

Low Estrogen

Estrogen supports vaginal lubrication, blood flow to genital tissues, and overall arousal. Low estrogen - common in perimenopause, postpartum, and while breastfeeding - can make sex uncomfortable, which naturally reduces desire.

Progesterone Imbalance

Progesterone affects mood, sleep, and relaxation. Both high and low levels can impact libido indirectly through their effects on mood and energy.

Thyroid Dysfunction

Both hypothyroidism and hyperthyroidism are associated with sexual dysfunction. A study in the *Journal of Clinical Endocrinology & Metabolism* found that thyroid disorders significantly impaired desire, arousal, and satisfaction in women (Carani et al., 2005).

What to test: - TSH - Free T3 - Free T4 - Thyroid antibodies

Nutrient Deficiencies

Iron and Ferritin

Iron deficiency causes fatigue that makes everything harder - including wanting sex. When you're exhausted, libido is one of the first things to go.

Vitamin D

Research in the *International Journal of Endocrinology* has linked vitamin D deficiency to female sexual dysfunction, possibly through its effects on hormone production and mood regulation (Krysiak et al., 2018).

B12

Deficiency causes fatigue, mood changes, and neurological symptoms - all of which can suppress desire.

The Low Libido Lab Panel

Core Tests - Total and Free Testosterone - SHBG - Estradiol - Progesterone - DHEA-S

Thyroid - TSH, Free T3, Free T4 - Thyroid antibodies

Nutrients - Ferritin - Vitamin D - Vitamin B12

Metabolic - Fasting glucose and insulin (blood sugar crashes affect energy and mood) - Cortisol (chronic stress suppresses sex hormones)

When to Test

For premenopausal women, test hormones on days 3-5 of your cycle for baseline levels. Testosterone is highest in the morning, so early testing is preferred.

Beyond the Lab

Lab results provide data, but context matters. Medications (especially SSRIs and hormonal contraceptives), relationship factors, stress, and sleep quality all influence desire. Addressing physical imbalances often creates the foundation for other interventions to work.

References

• Shifren, J. L., et al. (2008). Sexual problems and distress in United States women. *Obstetrics & Gynecology*, 112(5), 970-978.
• Davis, S. R., et al. (2008). Testosterone for low libido in postmenopausal women not taking estrogen. *New England Journal of Medicine*, 359(19), 2005-2017.
• Zimmerman, Y., et al. (2014). The effect of combined oral contraception on testosterone levels in healthy women. *Contraception*, 90(1), 18-21.
• Carani, C., et al. (2005). Female sexuality and thyroid disorders. *Journal of Clinical Endocrinology & Metabolism*, 90(4), 2120-2126.
• Krysiak, R., et al. (2018). Vitamin D and sexual function in women. *International Journal of Endocrinology*, 2018, 8525104.