Are You Missing This Key Nutrient? Thiamine Deficiency Symptoms to Know.

Byscott

Updated May 17, 2025

What are the symptoms of thiamine deficiency?

If you were wondering what a lack of thiamine actually feels like, the answer is: complicated. This isn’t the kind of deficiency that shows up with just one telltale sign. It tends to sneak in, scatter symptoms across different systems, and make you think it’s something else entirely.

One of the earliest signs? Fatigue. Not your typical “I stayed up too late” kind of tired, but a deep, hard-to-shake exhaustion. People often describe it as a persistent heaviness, physically and mentally. That might come along with irritability, trouble concentrating, or feeling mentally “foggy.”

As it progresses, more specific symptoms start to emerge. Muscle weakness is common—especially in the legs. You might notice you’re clumsier than usual or have trouble walking steadily. In some cases, there’s a strange tingling or numbness in the hands and feet, a sign that your nerves aren’t firing quite right.

Thiamine also supports healthy digestion, so you might experience loss of appetite or nausea. And because the heart needs thiamine to function properly, a serious deficiency can lead to heart palpitations or a rapid heartbeat. In more advanced cases, it may even cause shortness of breath or swelling due to fluid retention.

There are also two major medical conditions linked to severe thiamine deficiency: beriberi and Wernicke-Korsakoff syndrome. Beriberi affects the cardiovascular and nervous systems, while Wernicke-Korsakoff impacts the brain and can cause confusion, memory problems, and even hallucinations. These are more common in people with chronic alcohol use, but they’re not exclusive to that group.

Why would someone become thiamine deficient?

You’d think in a modern diet this wouldn’t happen often—but it does. Chronic alcohol consumption is one of the biggest culprits, because alcohol interferes with thiamine absorption and storage. But other risk factors include gastrointestinal conditions like Crohn’s disease or bariatric surgery, both of which affect nutrient absorption.

Older adults, people with diabetes, and those eating highly processed or restricted diets may also be at risk. Breastfeeding individuals, especially if they’re not getting enough thiamine themselves, can experience deficiency too—and so can their babies.

Even high levels of stress or illness can burn through your thiamine stores faster than usual. Basically, if your body is in overdrive, it might need more B1 than you’re getting.

The Takeaway

Thiamine deficiency is sneaky—and more common than most people think. The symptoms are varied and easy to overlook, which makes it all the more important to tune into how your body feels. If you’ve been dealing with unexplained fatigue, brain fog, or muscle weakness, it might be worth checking in on your B-vitamin levels.

Thiamine is water-soluble, which means your body doesn’t store much of it. You need a steady supply through food (like whole grains, legumes, and meats) or supplements. And while a deficiency is treatable, catching it early makes all the difference.