Thyroid problems may cause unexplained weight gain, hair loss, and fatigue to occur together. You may also have an iron or vitamin deficiency. Other symptoms may offer a clue as to the cause and help a doctor make a diagnosis.

When you experience multiple symptoms such as weight gain, hair loss, and fatigue at the same time, you may feel confused and anxious. You may wonder if it’s a mere coincidence or a genuine health concern.

Weight gain, hair loss, and fatigue are often linked to stress, diet, and lifestyle changes. Medical conditions, such as thyroid dysfunction and iron deficiency anemia, can sometimes also be the cause.

Consider speaking with a doctor to find out if your symptoms are related to a medical condition. Below, we discuss the different medical conditions that may cause these symptoms and what you can do to treat them.

Language matters

Sex and gender exist on spectrums. In this article, we sometimes use “male” and “female” or “men” and “women” to reflect the language used by the sources we cite. Your gender identity may not align with how your body responds to these conditions.

Learn more about sex and gender.

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Hypothyroidism, also called “underactive thyroid,” occurs when your thyroid gland doesn’t produce enough thyroid hormone. The thyroid hormone has multiple roles that regulate:

  • metabolism
  • growth
  • contraction of skeletal muscles
  • heart rate

Some symptoms of hypothyroidism, such as brittle hair, weight gain, and fatigue, develop gradually. Some people may notice them after several years.

Your hair follicles have thyroid hormone receptors that play a role in the hair growth cycle. Impaired thyroid function may affect the frequency of your hair’s active growth phase.

Low thyroid hormone levels can increase your cholesterol levels, reduce fat breakdown, and slow down your metabolism. According to the American Thyroid Association, hypothyroidism-related weight gain is usually due to a buildup of salt and water in your body. Most people gain about 5 to 10 pounds.

Your thyroid also helps to regulate your body’s energy demands, so reduced thyroid function can lead to fatigue.

Other common symptoms of hypothyroidism include:

How to treat hypothyroidism

If a doctor suspects you have hypothyroidism, they may order a thyroid function test to measure hormone levels in your blood. If results suggest you have hypothyroidism, they may prescribe levothyroxine, a synthetic hormone.

You can also try to reduce stress and add missing nutrients to your diet.

Learn more about natural remedies for hypothyroidism.

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Hyperthyroidism is the opposite of hypothyroidism. People with this condition have higher than typical thyroid levels. Also called “overactive thyroid,” this condition is more common in women ages 20 to 40.

Hyperthyroidism ramps up your metabolism. Increased metabolism can disrupt sleep and affect your energy levels and mood, leading to fatigue. This condition can also cause hair thinning.

Weight gain isn’t a common symptom of hyperthyroidism, but some people may experience it due to an increased appetite.

Hyperthyroidism can also cause:

  • anxiety
  • muscle weakness
  • pounding of the heart
  • irregular heart rate
  • trembling of the hands and fingers
  • changes in bowel patterns, particularly more frequent bowel movements
  • unusual sweating
  • weight loss

How to treat hyperthyroidism

Options for treating hyperthyroidism include:

  • antithyroid medications to reduce hormone production
  • radioiodine to shrink your thyroid gland and slow down its activity
  • beta-blockers to reduce heart symptoms
  • surgery to remove all or part of your thyroid gland
  • acupuncture to manage symptoms

Learn more about natural treatments for hyperthyroidism.

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Iron deficiency anemia occurs due to low amounts of iron in your blood. Your blood needs iron to produce hemoglobin, a protein that allows red blood cells to carry oxygen to different parts of your body.

When your cells lack oxygen, you can get tired and short of breath. Low energy and reduced metabolism can make it harder to exercise or burn calories, which may increase the chance of weight gain.

Iron deficiency can also affect cells that repair and stimulate hair growth, causing hair loss.

Other symptoms of iron deficiency include:

  • skin that looks paler than usual
  • brittle nails
  • chest pain

How to treat iron deficiency anemia

A doctor may suggest you take iron supplements to increase your iron supply. Restoration of iron levels may take about 3 to 6 months. Other options include:

  • blood transfusions to replace red blood cells
  • iron infusions to provide more iron to your blood
  • erythropoiesis-stimulating agent (ESA) to produce more red blood cells

Learn about iron-rich foods you can add to your diet.

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Vitamin B12, or cobalamin, is a natural vitamin found in foods, predominantly animal sources. This vitamin plays a vital role in:

  • brain function
  • nerve cell health
  • DNA production
  • red blood cell production

How much vitamin B12 you need varies by age. Pregnant and breastfeeding people need higher amounts of B12.

A condition called megaloblastic anemia, the hallmark of vitamin B12 deficiency, can cause fatigue and weakness. Megaloblastic anemia can also cause hair changes, including hair loss that may be due to an impairment in DNA synthesis.

Research on how vitamin B12 deficiency affects weight is mixed. The National Institutes of Health (NIH) notes that vitamin B12 deficiency tends to cause weight loss more than weight gain, but a 2020 review of studies suggests that low vitamin B12 levels may contribute to obesity in children and pregnant people.

How to treat vitamin B12 deficiency

Treatment for vitamin B12 deficiency will depend on the underlying cause. For instance, people with atrophic gastritis have a problem absorbing vitamin B12 from foods. A doctor can help you find the cause and appropriate treatment.

You can also take vitamin B12 supplements and eat vitamin B12-fortified grains.

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Diabetes is a chronic condition that causes high levels of glucose in your blood. Since diabetes affects the way your body converts food to energy, it may likely affect your weight. Diabetes weight gain may be due to increased calorie consumption and insulin therapy, a common diabetes treatment approach.

Diabetes can also cause fatigue and lethargy. The cells that need glucose for energy barely get enough.

Untreated diabetes can also damage your blood vessels, which makes it difficult for your blood to carry oxygen and nutrients to your cells, including your hair cells. This can lead to hair loss.

Other common symptoms of diabetes include:

  • frequent urinating
  • numbness or tingling sensation in the hands or feet
  • blurry vision
  • feeling thirsty
  • constant feeling of hunger

How to treat diabetes

Treatment for diabetes will depend on the type. People with type 1 diabetes need insulin therapy because their bodies don’t produce insulin.

People with type 2 diabetes may need to take medication such as metformin. Some people may only need lifestyle and dietary changes, such as regular exercise and eating whole, natural foods.

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It’s best not to overlook symptoms such as unexplained changes in weight, hair loss, and fatigue. Consider speaking with a doctor if you experience these symptoms, especially when they occur with other unusual symptoms.

These changes aren’t always the result of a medical condition. Still, it’s often best to seek medical attention, especially when these symptoms persist, to be sure your bodily functions aren’t impaired.

On the surface, weight gain, hair loss, and fatigue seem unrelated. If they occur at the same time, it may be due to an underlying medical condition. Consider speaking with a doctor about your symptoms.

A doctor may perform an examination and run some tests. If your symptoms aren’t linked to a health condition, they may suggest home remedies to help you get more energized, improve your hair health, or maintain a moderate weight if desired.