The thyroid sits at the front of the neck, just below the voice box, and is checked by gentle examination as well as blood tests. Image posed by models.
Picture this: you’re holding your breath, hoping for two pink lines to appear. The monthly emotional rollercoaster of trying to conceive brings hope, frustration, excitement, and anxiety. If this is your journey, know you're not alone.
What few people realise is that a tiny gland in your neck, the thyroid, plays a vital role. If you've focused on tracking ovulation, nutrition, and stress, don't overlook your thyroid.
This small, butterfly-shaped gland could be the missing piece in your fertility puzzle for both partners.
Why Thyroid Function Matters for Fertility
Recent research shows that thyroid disorders affect between 10 and 34 per cent of women of reproductive age, and they can significantly impact your ability to conceive.
The good news?
Thyroid function is something you can assess, optimise, and track. Your thyroid produces hormones that control metabolism and act like a maestro, ensuring every reproductive process follows the right tempo.
Imagine your reproductive system as an orchestra: when the thyroid maintains its rhythm, everything from ovulation to hormone signals, plays in harmony.
If the conductor falters, the whole ensemble goes out of sync, making conception more challenging.
For Women
Hypothyroidism (underactive thyroid) affects 2 to 4 percent of women in the reproductive age group.2 When your thyroid isn't producing enough hormones, several fertility challenges can emerge:
- Anovulatory Cycles: Insufficient thyroid hormone can disrupt the menstrual cycle, leading to irregular ovulation and anovulation (cycles in which no egg is released by the ovaries), making it difficult to time conception.2
- Luteal Phase Defects: The luteal phase is the time after ovulation when your uterine lining prepares for implantation (when a fertilised embryo attaches to the uterus). Hypothyroidism can cause luteal phase defects, meaning the uterine lining doesn't develop properly to support a pregnancy.2
- Hyperprolactinemia (Elevated Prolactin): Hypothyroidism is linked to increased TRH (thyrotropin-releasing hormone) secretion, which stimulates the pituitary gland to secrete TSH (thyroid-stimulating hormone) and prolactin (a hormone involved in milk production and fertility). Elevated prolactin negatively impacts fertility by disrupting the natural rhythm of GnRH (gonadotropin-releasing hormone, which starts the release of other reproductive hormones), thereby affecting ovarian function.2
- Increased Miscarriage Risk: Both hypothyroidism and hyperthyroidism can affect the success rates of fertility treatments and may be associated with lower implantation rates (when an embryo attaches to the womb) and an increased risk of miscarriage.3,4
Key Takeaway: Thyroid dysfunction and autoimmunity directly impact fertility and pregnancy outcomes, making timely assessment and management vital for both natural and assisted conception.
For Men
Male factor infertility contributes to 40 to 50 percent of conception challenges, yet thyroid health is often overlooked in fertility discussions for men.
- Reduced Sperm Quality: Hyperthyroidism (overactive thyroid) has been associated with reduced semen volume (amount of fluid in an ejaculate), reduced sperm density (number of sperm per millilitre), motility (how well they move), and morphology (shape), while hypothyroidism (underactive thyroid) is associated with abnormal sperm shape (morphology).5,6
- Hormonal Imbalances: Both hypothyroidism and hyperthyroidism adversely affect male reproductive organs and fertility, with studies showing low sperm counts and decreased sperm motility that can be corrected when thyroid disease is treated.5
- Erectile and Ejaculatory Dysfunction: Both hypothyroidism and hyperthyroidism can cause ejaculation and erectile dysfunction in men.7
- Oxidative Stress: Thyroid disorders can cause oxidative stress (an imbalance between harmful molecules called free radicals and antioxidants, which protect cells), which can damage sperm DNA and reduce sperm motility (the ability of sperm to move and swim properly).6
The timeline matters: sperm takes approximately 74 days to mature, so optimising thyroid function now affects sperm quality in 2 to 3 months.5
The Vicious Cycle
Here's what happens when thyroid dysfunction goes unaddressed:
- Thyroid hormone imbalance → disrupts ovulation or sperm production.
- Hormonal cascade effects → elevated prolactin, luteal phase defects, or testosterone changes
- Difficulty conceiving → stress and frustration increase
- Chronic stress → further suppresses thyroid function and reproductive hormones.
- Cycle continues ↻
Key Takeaway: Addressing thyroid-related fertility challenges enables most women to conceive within a year with proper treatment. Early action is essential for success.
Quick Wins: 5 Changes You Can Make This Week
You do not need to make major changes all at once. Begin with these evidence-based steps, which can make a positive difference within days:
1. Get Your Thyroid Tested
Key Takeaway: Aim for a TSH below 2.5 mIU/L for conception. Consistent monitoring can significantly improve your fertility outcomes.
Quick action: Call your doctor this week and request a comprehensive thyroid panel, including TSH (thyroid-stimulating hormone), free T3 (triiodothyronine), free T4 (thyroxine), and thyroid antibodies (TPO—thyroid peroxidase, and thyroglobulin). If you're already trying to conceive, ask about the optimal TSH range for fertility instead of the general population range.
If your doctor is hesitant to order the full thyroid panel or suggests only checking TSH, you can explain that recent fertility guidelines often recommend a more thorough evaluation of thyroid function when conception is the goal.
Mention any symptoms you may be experiencing, family history, or history of difficulty conceiving. If your doctor still resists, consider seeking a second opinion, requesting a referral to an endocrinologist or reproductive specialist, or requesting a written explanation of the recommended approach. Remember, your health and peace of mind matter—it's okay to advocate respectfully for the testing and answers you need.
2. Eat 2 Brazil Nuts Daily for Selenium
Key Takeaway: Selenium supports thyroid health and hormone synthesis—two essentials for optimising fertility.
Quick action: Add exactly 2 Brazil nuts to your daily routine (morning with breakfast is easiest). Just 2 nuts provide about 140 mcg of selenium, which is close to the recommended 200 mcg for thyroid support.
More is not better, as excessive selenium can be harmful. If you already take a prenatal or multivitamin, check the label for selenium content so you do not exceed the recommended amount when combined with these nuts. Alternatively, eat selenium-rich foods like wild-caught fish (3-4 servings weekly), eggs, mushrooms, and oats.
3. Prioritise 7 to 9 Hours of Sleep in a Dark, Cool Room
Key Takeaway: High-quality sleep helps regulate thyroid rhythms and hormones crucial for fertility.
Quick action: Set a consistent bedtime tonight that allows for 8 hours of sleep.
Make your bedroom completely dark (blackout curtains or an eye mask), keep the temperature between 60°F and 67°F (15 °C and 19°C), and remove all screens 1 hour before bed.
If you wake to use the bathroom, use red light only, since blue light from phone screens suppresses melatonin and disrupts thyroid rhythm. Keeping your room dark helps your body produce steady melatonin, which not only supports thyroid function but also helps GnRH, the key hormone that initiates the reproductive hormone cascade, stay on schedule.
This means better sleep hygiene directly supports your fertility at a hormonal level.
4. Add Zinc-Rich Foods to Every Meal
Key Takeaway: Zinc is crucial for healthy thyroid hormone production and successful conception.
Quick action: Include one zinc-rich food at each meal this week.
Options include oysters (the highest source), grass-fed beef, lamb, chicken, pumpkin seeds (2 tablespoons provides 2-3 mg of zinc), cashews, chickpeas, or plain yoghurt.
Aim for 8 to 11 mg of zinc daily from food. If you choose to supplement, use zinc picolinate or citrate (15-25 mg per day) with food to prevent nausea.
If you already take a multivitamin or prenatal supplement, check the label for zinc content before adding a separate zinc supplement.
It is always best to check with your doctor before combining supplements, since too much zinc over time can lower copper levels (another important mineral) and impair immunity. Exceeding 40 mg daily for long periods may be harmful. Avoid long-term high-dose supplementation without testing, as it can create imbalances between different minerals in the body.
5. Test and Optimise Your Vitamin D Level
Key Takeaway: Optimal vitamin D levels support immune balance, reduce thyroid antibodies, and encourage fertility.
Quick action: Request a 25-OH vitamin D test if you haven't had one in the past 6 months.
Optimal levels for fertility are 50 to 80 ng/mL (not just "normal", which can be as low as 30 ng/mL).
If deficient, supplement with vitamin D3 (2,000-4,000 IU daily with a fat-containing meal for absorption) and retest in 8 to 12 weeks.
Get 15 to 20 minutes of midday sun exposure on bare arms and legs 3 to 4 times weekly when possible.
Check with your doctor before starting any supplement, especially if you're on thyroid medication
The Male Factor
Male factor infertility contributes to 40 to 50 percent of conception challenges, yet thyroid health for men is often completely ignored in fertility workups.
Why Thyroid Matters for Male Fertility
Guidelines recommend screening for thyroid disorders in men with ejaculation and erectile dysfunction and/or altered semen parameters.
Research shows that both hypothyroidism and hyperthyroidism can significantly impact male reproductive function.
The sperm maturation timeline is crucial: sperm take approximately 74 days to fully develop. This means that optimising thyroid function today will affect sperm quality in your partner's semen analysis 2 to 3 months from now.
Key Takeaway
Both partners should have their thyroid function checked when trying to conceive. This is a team effort. Studies show that abnormalities in sperm morphology and motility caused by thyroid dysfunction were corrected when patients were treated for thyroid disease.
When to Seek Professional Help
While lifestyle changes can significantly improve thyroid function and fertility, some situations require medical attention:
- TSH above 2.5 mIU/L when trying to conceive or above 4 mIU/L in general
- Irregular or absent menstrual cycles for more than 3 months
- Two or more miscarriages
- Difficulty conceiving after 6 months of trying (if over 35) or 12 months (if under 35)
- Family history of thyroid disease, especially autoimmune thyroid conditions
- Symptoms like fatigue, weight changes, cold intolerance, hair loss, or brain fog
- Known thyroid antibodies or diagnosed thyroid condition
- For men: abnormal semen analysis or sexual dysfunction
Are you ready to take the next step?
Optimising thyroid function is a powerful foundation for fertility, but it's just one piece of the puzzle. Our Fertility Foundations+ Program takes a comprehensive approach, addressing metabolic health, thyroid function, mitochondrial support, and genetic factors, all guided by a doctor and specialist nutritionist. (Coming Soon)
The Bottom Line
Thyroid function isn't just about metabolism, it's fundamental to reproductive health for both women and men. Thyroid dysfunction is frequently associated with female infertility, and emerging evidence shows its impact on male fertility as well.11
By implementing even a few of the strategies above, you're taking meaningful action to support your fertility naturally. Research shows that proper thyroid management can restore normal ovulation, improve sperm quality, and increase conception rates.
Remember: Small, consistent changes often work better than dramatic overhauls. Start with one or two quick wins this week, get your TSH tested and add those Brazil nuts to your breakfast, and build from there. Your body is designed to conceive. Sometimes it just needs the right conditions and that starts with a properly functioning thyroid. This information is for educational purposes and does not replace personalised medical advice. Always consult with your healthcare provider before making changes to your health routine, especially if you're currently undergoing fertility treatment or taking thyroid medication.
Medical References & Appendix
Additional Supporting Research
TSH Optimal Ranges for Fertility:
- Zhou, D., Deng, H., Li, R., Huang, Y., Li, Y., Zhu, H., Yang, X., Xia, M., & Ye, H. (2022). The relationship between TSH levels and clinical pregnancy outcomes for patients who undergo in vitro fertilisation/intracytoplasmic sperm injection. Translational Paediatrics, 11(5), 690-697.
Selenium and Thyroid:
- Ventura, M., Melo, M., & Carrilho, F. (2017). Selenium and Thyroid Disease: From Pathophysiology to Treatment. International Journal of Endocrinology, 2017, 1297658.
Male Thyroid and Fertility:
- Krassas, G.E., & Perros, P. (2003). Thyroid disease and male reproductive function. Journal of Endocrinological Investigation, 26, 372-380.
Thyroid Autoimmunity:
- Bucci, I., Giuliani, C., Di Dalmazi, G., Formoso, G., & Napolitano, G. (2022). Thyroid Autoimmunity in Female Infertility and Assisted Reproductive Technology Outcome. Frontiers in Endocrinology, 13, 768363.
Clinical Guidelines Referenced
- American Thyroid Association (ATA): Guidelines for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum
- American Society for Reproductive Medicine (ASRM): 2024 Subclinical Hypothyroidism Guideline
- European Thyroid Association: Guidelines on Thyroid Disorders Prior to and During Assisted Reproduction
- Endocrine Society: Clinical Practice Guidelines on Thyroid Disease and Pregnancy
Footnotes
- Joshi, J.S., Choudhary, N., Mahajan, S., & Khemani, S. (2024). From Conception to Delivery: A Comprehensive Review of Thyroid Disorders and Their Far-Reaching Impact on Feto-Maternal Health. Cureus, 16(2), e53144. doi: 10.7759/cureus.53144
Key Finding: Thyroid disorders affect 10.4-33.9% of women of reproductive age, with hypothyroidism being more common than hyperthyroidism.
Full Text: https://pmc.ncbi.nlm.nih.gov/articles/PMC10907906/ - Verma, I., Sood, R., Juneja, S., & Kaur, S. (2012). Prevalence of hypothyroidism in infertile women and evaluation of the response of treatment for hypothyroidism on infertility. International Journal of Applied and Basic Medical Research, 2(1), 17-19. doi: 10.4103/0976-5484.95177
Key Finding: Prevalence of hypothyroidism was 23.9% in infertile women; 76.6% conceived after thyroid treatment. Hypothyroidism affects fertility through anovulatory cycles, luteal phase defects, and hyperprolactinemia.
Full Text: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3657979/ - Monteleone, P., Parrini, D., Faviana, P., Carletti, E., Casarosa, E., Uccelli, A., Cela, V., & Artini, P.G. (2020). Impact of thyroid disease on fertility and assisted conception. Best Practice & Research Clinical Endocrinology & Metabolism, 34(1), 101323. doi: 10.1016/j.beem.2019.101323
Key Finding: Thyroid autoimmunity and thyroid dysfunction are independently associated with adverse fertility and pregnancy outcomes in spontaneous conception and after ART.
Full Text: https://pubmed.ncbi.nlm.nih.gov/32037280/ - Dosiou, C. (2020). Thyroid and Fertility: Recent Advances. Thyroid, 30(4), 479-486. doi: 10.1089/thy.2019.0382
Key Finding: Recent studies confirm associations of TSH elevation and/or thyroid autoimmunity with infertility and low ovarian reserve. TSH >4 mIU/L treatment benefit confirmed in large retrospective cohort studies.
Full Text: https://pubmed.ncbi.nlm.nih.gov/31903865/ - Krajewska-Kulak, E., & Sengupta, P. (2013). Thyroid Function in Male Infertility. Frontiers in Endocrinology, 4, 174. doi: 10.3389/fendo.2013.00174
Key Finding: Changes in normal thyroid function led to decreased sexual activity and fertility in men. Hypothyroidism adversely affects male fertility with abnormal sperm morphology and decreased motility. Treatment corrects these abnormalities.
Full Text: https://pmc.ncbi.nlm.nih.gov/articles/PMC3826086/ - La Vignera, S., & Vita, R. (2018). Thyroid dysfunction and semen quality. International Journal of Immunopathology and Pharmacology, 32, 2058738418775241. doi: 10.1177/2058738418775241
Key Finding: Hyperthyroidism associated with reduced semen volume, sperm density, motility, and morphology. Hypothyroidism associated with reduced sperm morphology. Thyroid function tests should be part of diagnostic workup for infertile men.
Full Text: https://pmc.ncbi.nlm.nih.gov/articles/PMC5946587/ - Anelli, V., Gatta, E., Pirola, I., Delbarba, A., & Cappelli, C. (2024). Thyroid impairment and male fertility: a narrative review of literature. The Aging Male, 27(1), 2310303. doi: 10.1080/13685538.2024.2310303
Key Finding: Guidelines recommend screening for thyroid disorders in men with ejaculation/erectile dysfunction and/or altered semen parameters. Both hypothyroidism and hyperthyroidism can cause sexual dysfunction.
Full Text: https://www.tandfonline.com/doi/full/10.1080/13685538.2024.2310303 - American Society for Reproductive Medicine Practice Committee. (2024). Subclinical hypothyroidism in the infertile female population: a guideline. Fertility and Sterility, 121, 765-782. doi: 10.1016/j.fertnstert.2024.02.022
Key Finding: For women of childbearing age planning pregnancy, TSH should be maintained below 2.5 mIU/L. Classic definition of subclinical hypothyroidism is TSH >4.5-5.0 mIU/L with normal free thyroxine.
Full Text: https://www.asrm.org/practice-guidance/practice-committee-documents/subclinical-hypothyroidism-in-the-infertile-female-population-a-guideline/ - Vissenberg, R., Manders, V.D., Mastenbroek, S., Fliers, E., Afink, G.B., Ris-Stalpers, C., Goddijn, M., & Bisschop, P.H. (2018). Higher TSH Levels Within the Normal Range Are Associated With Unexplained Infertility. The Journal of Clinical Endocrinology & Metabolism, 103(2), 632-639. doi: 10.1210/jc.2017-02045
Key Finding: Women with unexplained infertility had significantly higher TSH levels (median 1.95 vs 1.66 mIU/L, p=0.003). Nearly twice as many women with unexplained infertility (26.9%) had TSH ≥2.5 mIU/L compared to controls (13.5%).
Full Text: https://pmc.ncbi.nlm.nih.gov/articles/PMC5800836/ - Mahmoodianfard, S., Vafa, M., Golgiri, F., Khoshniat, M., Gohari, M., Solati, Z., & Djalali, M. (2015). Effects of Zinc and Selenium Supplementation on Thyroid Function in Overweight and Obese Hypothyroid Female Patients: A Randomized Double-Blind Controlled Trial. Journal of the American College of Nutrition, 34(5), 391-399. doi: 10.1080/07315724.2014.926161
Key Finding: 12-week supplementation with 30mg zinc and/or 200mcg selenium showed improvement in thyroid function in hypothyroid women. Zinc increased the FT3/FT4 ratio, reflecting improved conversion.
Full Text: https://pubmed.ncbi.nlm.nih.gov/25758370/ - Mintziori, G., Mousiolis, A., Duntas, L.H., & Goulis, D.G. (2023). The role of thyroid function in female and male infertility: a narrative review. Journal of Endocrinological Investigation, 46, 15-26. doi: 10.1007/s40618-022-01883-7
Key Finding: Thyroid dysfunction is frequently associated with female infertility and emerging evidence shows impact on male fertility. Thyroid function should be monitored in both male and female partners seeking pregnancy.
Full Text: https://pmc.ncbi.nlm.nih.gov/articles/PMC9829629/ - Baeke, F., Takiishi, T., Korf, H., Gysemans, C., & Mathieu, C. (2010). Vitamin D: modulator of the immune system. Current Opinion in Pharmacology, 10(4), 482-496. doi: 10.1016/j.coph.2010.04.001
Key Finding: Vitamin D deficiency associated with autoimmune thyroid conditions including Graves' disease and Hashimoto's disease. Vitamin D acts as immune system modulator.
Referenced in: NP Thyroid Nutrients Guide. https://npthyroid.com/tipsresource/nutrients-for-better-thyroid-function/
This page is general information and does not replace personal medical advice. Dr Jean-Marc Sobczyk, GMC 6148690.