Young woman sitting on grassy hill while wondering, "Why do I have low mood?"

Feeling Blue Lately? Here's What Could Be Behind Your Low Mood

Updated January 17, 2024.

A low mood can be your body’s way of telling you that your hormones are out of balance – or that you aren’t getting the vitamins you need. So if you’re feeling down, keep reading to learn more about the hormone imbalances and vitamin deficiencies that could be lurking behind that blue mood.

(1) An Underactive Thyroid Gland (Hypothyroidism)

The thyroid gland, which sits at the front of the neck, regulates many of the body’s everyday functions – from your body temperature to your metabolism. It does this by pumping out thyroid hormones – or “chemical messengers” – into the bloodstream. The bloodstream carries these hormones to other parts of your body. This allows the thyroid to control different processes in your body from a distance.

But what happens if your thyroid doesn’t work properly – and can’t pump out very many “chemical messengers” into the bloodstream?

If that happens, the thyroid loses its ability to regulate key functions in your body. This is a condition known as “hypothyroidism” (or underactive thyroid), which can sink your mood and make you feel depressed [1].

What causes hypothyroidism in the first place? In the United States, the #1 cause of hypothyroidism is an autoimmune disorder known as Hashimoto's disease [2] – affecting an estimated 1 in 20 people. (Autoimmune disorders occur when your immune system – which is supposed to protect you – backfires on your body and attacks some of your tissues, glands, and organs.) An iodine deficiency can also result in hypothyroidism because your thyroid needs iodine to build hormones.

Signs that you might have hypothyroidism include:

  • Weight gain
  • Constipation
  • Sensitivity to cold or heat
  • Tiredness
  • Hair loss, often marked by dry or thinning hair
  • Problems with memory
  • Heavy, absent, or irregular menstrual periods
  • Frequent sweating
  • Difficulty sleeping

One way you can see if your thyroid might be underactive – and potentially the reason behind your low spirits? Give your thyroid hormone levels a checkup from the convenience of home with our at-home thyroid test– and consult with your doctor about any abnormal results.

(2) B Vitamin Deficiency

Several B vitamins – like B6 vitamins, B9, and B12 – play important roles in your brain chemistry. So a deficiency in any of these B vitamins can send you right into the doldrums. Scientific research reinforces this point: studies show that people with depression are more likely to have low levels of B9 (also known as folate or folic acid) and B12 [3].

A number of things can trigger a B vitamin deficiency, such as excessive alcohol consumption or a gut malabsorption condition (like Crohn's disease, ulcerative colitis, or celiac disease). Certain dietary restrictions can also up the odds of a B vitamin deficiency: a vegan or vegetarian diet can leave you with inadequate levels of B12 because this vitamin isn’t naturally found in plant-based food.

Some signs that you may have a B vitamin deficiency include:

  • Cracks or sores in the corners of the mouth
  • A swollen tongue, or a smooth-looking tongue
  • Tiredness
  • An increase in gray hair
  • A tingly or numb feeling in your hands and feet
  • Blurry vision
  • Dizziness
  • Loss of breath or shortness of breath
  • A red, itchy rash on the upper body or face


Vitamin D and B vitamin deficiencies – as well as thyroid hormone imbalances – can suck the joy out of your mood and leave you feeling blue. However, various at-home tests from Everlywell can help you discover your body’s vitamin deficiencies and hormone imbalances – and put you on track to greater well-being. And – if you’ve been hunting around for the reason behind your low mood – don’t forget to share any abnormal test results with your doctor to learn what your next steps should be.

Everlywell makes lab testing easy and convenient with at-home collection and digital results in days. Learn More