You notice it first in the shower. More hair in the drain than there used to be. Then it's the brush, or your ponytail feeling thinner, or a wider part when you look in the mirror. It's easy to brush it off as "just aging," but if it feels sudden or out of proportion, your body may be telling you something.

In my practice, hair thinning is one of the most common concerns I hear from women in their 40s, and it's often met with a shrug or a bottle of biotin. Hair is a bit like a canary in a coal mine. It's not essential for survival, so when your body is short on resources or under stress, hair is one of the first things it quietly deprioritizes.

Why Hair Is Such a Sensitive Signal

Each hair follicle goes through a cycle of growing, resting, and shedding. Many things can push more follicles into the shedding phase at once, and the shedding often shows up two to three months after the trigger. That delay is why it can be hard to connect the dots on your own.

Here are the six areas I look at first.

1. Low Iron Stores (Ferritin)

This is the one I see most often. You can have a normal hemoglobin and still have low iron stores, and hair follicles need those stores to grow well. Fatigue, cold hands, and shortness of breath on stairs often travel alongside it. Many labs also flag ferritin as "normal" at levels that are too low for healthy hair. I go deeper in Your Iron Panel Says You're Not Anemic.

2. A Sluggish or Autoimmune Thyroid

Thyroid hormone helps regulate the hair growth cycle. When it's out of balance, hair can become thin, dry, and brittle, and you may notice outer eyebrow thinning too. A TSH-only screen can miss the fuller picture, which is why I like to look at Free T3, Reverse T3, and thyroid antibodies. See Your Thyroid Labs Came Back "Normal".

3. Shifting Estrogen, Progesterone, and Androgens

During perimenopause, estrogen and progesterone decline and fluctuate, while the relative influence of androgens can rise. For some women, that means hair on the scalp gets finer and thinner, especially around the part and temples. You may also notice changes in your cycle, sleep, or mood. A single hormone test can easily miss the pattern, as I explain in Told You're "Too Young" for Perimenopause?

4. Blood Sugar and Insulin Resistance

When insulin runs high, it can affect hormone balance and increase inflammation, both of which can influence hair. If you're also dealing with afternoon crashes, sugar cravings, or stubborn weight gain, this deserves a look. Fasting glucose alone often looks fine, so I like to check fasting insulin and A1C. Start with Your Blood Sugar Is "Normal".

5. Chronic Stress and Cortisol Disruption

A major stressor, such as illness, surgery, a death in the family, or months of poor sleep, can trigger a wave of shedding a few months later. Ongoing stress can keep the same process simmering in the background. If you feel wired and tired, my post on cortisol rhythm may sound familiar.

6. Low Protein and Key Nutrients

Hair is made of protein, and many busy women simply don't eat enough of it, especially at breakfast. Low vitamin D, zinc, B12, and other nutrients can matter too. Sometimes the issue isn't the diet itself but absorption. Bloating, reflux, or irregular digestion can mean you're not getting the full benefit of what you eat. The 7 Lifestyle Levers That Quietly Transform Gut Health is a gentle place to begin.

Other Things Worth Ruling Out

Some medications, recent rapid weight loss, postpartum changes, tight hairstyles, and scalp conditions can all contribute. Hair loss can also be genetic, and that's okay to name. The goal isn't to blame yourself. It's to find out what's modifiable so you can support your body well.

What I Might Test

There's no single "hair loss panel," so I choose labs based on your story. Depending on your history, I may look at:

  • Ferritin and a full iron panel

  • A complete thyroid panel, including Free T3, Reverse T3, and antibodies

  • Fasting insulin and A1C, not only fasting glucose

  • Vitamin D, B12, and zinc

  • Hormone markers, timed to your cycle if you're still menstruating

  • Inflammation markers and, when indicated, gut testing

We also build a timeline: when the shedding started, what happened two to four months earlier, and what else has changed in your energy, sleep, digestion, and cycle.

Where to Start This Week

Before you add another supplement, try these steps for a few weeks:

  • Eat 25 to 30 grams of protein at breakfast. It supports hair and steadies blood sugar.

  • Ask for your ferritin number, not just "normal." Keep a copy of your labs so we can compare trends.

  • Go easy on hair. Loosen tight styles, lower the heat, and be gentle when wet.

  • Walk after meals. Ten minutes helps blood sugar and stress.

  • Protect your sleep. A regular bedtime does more for your hair than most serums.

  • Take a photo of your part monthly in the same light. It's the easiest way to see real change.

A word of caution: high-dose biotin can interfere with some lab tests, including thyroid and hormone results. If you take it, let your provider know before any blood draw.

When to Get More Help

If you notice sudden patchy hair loss, a painful or itchy scalp, or hair loss with major fatigue, unexplained weight changes, or irregular bleeding, please see a medical provider promptly.

For many women, though, thinning hair is a real signal, not vanity. When we look for patterns instead of dismissing the symptom, the path forward often gets much clearer. If you'd like help getting to the root of your hair, energy, and hormones, click the link below to connect with me.

This article is for educational purposes and isn't a substitute for personalized medical advice.