10 Surprising Reasons for Low Milk Supply (That Have Nothing to Do with Your Diet)

When milk supply feels low, it's easy to blame your water intake or wonder if you’re eating enough oatmeal. But while nutrition matters, it’s far from the full picture.

In reality, many hormonal, anatomical, and medical factors can impact milk production—and they’re often overlooked. If you’ve been doing “all the right things” and still feel like your supply is struggling, keep reading. These 10 surprising reasons might shed light on what’s really going on.

1. Thyroid Dysfunction - Even mild hypothyroidism or Hashimoto’s (an autoimmune thyroid condition) can interfere with lactation. The thyroid plays a key role in metabolism and milk-making hormones like prolactin and oxytocin. If you feel tired, cold, moody, or foggy in addition to low supply—your thyroid could be the missing link.

👉 Pro Tip: Ask your provider to check a full thyroid panel, not just TSH. Functional levels for breastfeeding may differ from "normal" lab ranges.

2. Retained Placental Fragments - If a small piece of placenta (or membrane) remains in the uterus after birth, it can interfere with the hormonal shift that signals milk to come in fully. This is especially relevant for parents who experience low supply from the start or for those whose milk never came in. Lab tests can help screen for this but generally imaging is recommended for diagnosis.

📍Often missed unless there's bleeding, pain, or ultrasound imaging.

3. Insufficient Glandular Tissue (IGT) - Some breasts don’t develop enough milk-making (glandular) tissue during puberty or pregnancy. This isn’t your fault—and has nothing to do with breast size—but it can limit supply potential.

🔎 Some clues include wide breast spacing, tubular shape, or lack of breast changes in pregnancy/postpartum.

4. Polycystic Ovary Syndrome (PCOS) - PCOS can disrupt hormones like estrogen, progesterone, and insulin—all of which impact lactation. Some people with PCOS make more than enough milk, but others struggle with chronic low supply, especially early on.

💡 PCOS is also associated with insulin resistance, which may affect prolactin response.

5. Low Prolactin Levels - Prolactin is the key hormone that tells your body to make milk. If it’s too low—due to certain medications, health conditions, or a poor hormonal feedback loop—you may not produce enough milk despite frequent nursing or pumping.

🩺 Prolactin testing (preferably baseline and surge) can help identify this root cause.

6. Hormonal Birth Control - Estrogen-containing birth control (like the pill, patch, or ring) can decrease milk supply—especially when introduced early postpartum. Even some progestin-only options may reduce supply in sensitive individuals.

👶🏼 Always discuss birth control options with a lactation-informed provider.

7. Diabetes or Insulin Resistance - Blood sugar issues can disrupt lactation hormones and interfere with milk supply. This is especially common in people with PCOS, gestational diabetes or pre-existing type 2 diabetes.

🍭 Insulin and prolactin are tightly linked. Stable blood sugar = better hormonal balance for milk production.

8. Anemia or Iron Deficiency - Even without classic symptoms like fatigue or dizziness, low iron can reduce your body's ability to support robust milk production.

🩸 Ferritin (iron storage) levels below 50 ng/mL may impair supply, even if your hemoglobin is “normal.”

9. Nipple or Breast Surgery - Breast reductions, augmentations, or biopsies may affect nerves, ducts, or blood flow—any of which can reduce supply depending on the surgical technique and recovery.

🩹Some people can still make milk, but anatomy may limit full supply without additional support.

10. Pituitary Disorders or Sheehan’s Syndrome - Rare, but important: The pituitary gland produces prolactin and oxytocin. If it's damaged (for example, from severe postpartum hemorrhage), it may not send the right milk-making signals.

🧠Watch for lack of milk coming in after birth, extreme fatigue, or absent periods.

Final Thoughts:

Low milk supply is rarely caused by just one thing—and it’s almost never your fault. If you’ve been told to “just nurse more” or “drink more water” and still feel something’s off, don’t give up. You deserve a deeper, functional look at what’s really going on.

🩺 Need help reviewing labs or identifying root causes of low supply? I offer holistic lactation consults that combine evidence-based care with functional testing when needed. Find more info at: www.advancedlactationcare.com

📌 Related Reading:

• Functional Labs in Breastfeeding Medicine: Beyond the Basics

• How Medications Impact Milk Supply: What’s Safe, What’s Not

Disclaimer: This blog is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your healthcare provider or lactation professional for personalized guidance.