Why Autoimmune Symptoms Get Worse in Your 40s

By Tina Chagoury, Clinical Dietitian · 5 min read · 2026-08-24

If your autoimmune symptoms have intensified in your forties, there is a specific mechanism behind it, and it is not a coincidence.

If autoimmune problems have increased for you in your forties, there is a biological reason for it.

Autoimmune disease is what happens when the immune system begins attacking your own tissue. In Hashimoto's thyroiditis, it attacks the thyroid gland. In rheumatoid arthritis, immune cells affect the joints.

The mechanism

During perimenopause, hormones do not simply fall. Before they decline, they fluctuate considerably. Oestrogen rises and drops in a way that is not remotely steady, while progesterone declines earlier and more gradually.

Now consider what each of these hormones does to immune function.

Oestrogen stimulates the immune system. Progesterone regulates and calms that response. They work as a pair.

So the imbalance that occurs naturally in perimenopause, with erratic oestrogen and falling progesterone, makes your immune signalling less stable. Susceptibility to inflammation rises considerably.

What else is happening at the same time

The hormonal picture is not the only change:

• Sleep is disrupted
• Cortisol patterns shift
• Gut health frequently deteriorates during this stage

All of that creates a more reactive internal environment.

What a flare looks like

This is why we see more flares in this decade. Women report:

• More joint pain
• Fatigue
• New sensitivities
• Food reactions
• Itching or skin changes

Often these appear without any obvious trigger, which is exactly what makes them confusing.

When to test, and what

If you have a family history of autoimmune disease, start monitoring yourself in your late thirties. Do not wait for your forties, and do not wait for symptoms.

If you have started to notice new fatigue, unexplained weight change, stiffness and joint pain, hair loss or skin changes, that is the point to test rather than wait.

Ask for:

• A full and complete thyroid panel, not TSH alone. That means Anti-TPO and Anti-TG antibodies as well as the standard markers.
• ANA
• hs-CRP and other inflammatory markers
• Vitamin D
• Iron status, including ferritin
• Fasting glucose and fasting insulin
• Gut assessment, particularly if you have digestive symptoms

Why early attention matters

The earlier we notice these changes, before they develop into a full condition, the more we can do with nutrition and lifestyle. Protocols such as the Autoimmune Protocol can help calm immune activity and reduce gut inflammation, and in some cases early intervention reduces the need for far more complex treatment later.

Stay aware, and pay attention to these patterns rather than explaining them away.

This article is nutrition education, not medical advice. Autoimmune diagnosis and treatment belong with your doctor. Nutrition supports medical care rather than replacing it.

Tina Chagoury is a licensed clinical dietitian specialising in women's hormonal health and the creator of the Hormone Reset Method™. Learn more and start here.