If you’ve ever stood beside an athlete prepping for a race, training session, or even a long week of high-intensity drills, you’ve probably heard mentions of micro-nutrients, protein goals, and hydration hacks. But one that flies under a lot of radars—until it’s missing—is vitamin B1, also called thiamine. As someone who’s spent the last decade working with athletes and formulating vitamin supplements (I’m the product lead at [my brand, no need to name], so I’ve talked to hundreds of endurance runners, soccer players, and CrossFit coaches about their nutrition gaps), I can tell you this: B1 isn’t just for preventing beriberi. For athletes, it’s a non-negotiable for keeping energy levels steady, supporting muscle function, and avoiding that dreaded mid-workout crash that makes you cut a session short. Let’s break down exactly what the recommended intake is for athletes, why it matters more than for non-athletes, and how you can make sure you’re getting enough (without overdoing it). Vitamin
First, let’s get the basics straight: what does vitamin B1 actually do, especially for someone moving their body at max effort? Its core job is converting the food you eat—carbs, mostly—into adenosine triphosphate (ATP), the molecule your body uses for immediate energy. For athletes, who rely heavily on carbs for fuel during long runs, bike rides, or team sports, that conversion is make-or-break. Without enough B1, your body can’t break down glycogen (the stored form of carbs in your muscles and liver) efficiently, so you’ll burn through energy way faster than you should. That’s why many endurance athletes report feeling fatigued, lightheaded, or shaky around the 60 to 90-minute mark of training—studies show that’s often a red flag of low thiamine levels. B1 also supports the health of nerve cells, which send signals to your muscles to contract, and helps reduce lactic acid buildup (the stuff that makes your legs burn during sprints). For anyone lifting heavy, doing high-rep circuits, or playing a sport that requires quick, sharp movements, that’s a huge deal.
Now, what’s the recommended intake for the average person? The Institute of Medicine (IOM) sets the Recommended Dietary Allowance (RDA) for adult men at 1.2 mg per day, and 1.1 mg per day for adult women. That’s enough for sedentary folks, who only need to cover basic metabolic functions. But athletes? Their needs go up. A 2019 study in the Journal of the International Society of Sports Nutrition found that endurance athletes—runners, cyclists, rowers—can require 30% to 50% more B1 than the RDA, putting their target at 1.5 to 1.8 mg per day. For team sport athletes, like soccer, basketball, or volleyball players, who have intermittent high-intensity efforts and slightly less steady carb intake than endurance athletes, the study found their needs are around 1.4 to 1.6 mg per day. And for strength athletes—powerlifters, weightlifters, CrossFit athletes—who rely on carbs for short, explosive bursts, the sweet spot is roughly 1.5 mg per day. That might not sound like a big jump, but when you’re training 5, 6, or even 7 days a week, that extra 0.3 to 0.6 mg is the difference between crushing a workout and tapering off early.
Wait, but why is that extra needed? Let’s talk about two key factors: increased energy turnover and sweat loss. When you exercise, your body’s metabolic rate spikes—sometimes up to 20 times the resting rate—so you’re burning through carbs at a much faster pace. That means you’re using more B1 to convert those carbs into energy. Then, there’s sweat. Thiamine is water-soluble, so when you sweat heavily, you lose small amounts of B1 through your skin. A 2021 study in Medicine & Science in Sports & Exercise found that athletes who sweat more than 1.5 liters per hour during training can lose up to 0.05 mg of B1 per liter of sweat. If you’re doing a 2-hour long run in hot weather, that’s an extra 0.1 mg lost just from sweat—enough to push you right below your target if you’re only hitting the RDA.
Before you start grabbing every B1 supplement off the shelf, let’s talk about how to get it from food first, because whole foods are always the best source. The top dietary sources of B1 are whole grains, lean pork, legumes, nuts, and seeds. Oatmeal, brown rice, lentils, and sunflower seeds are all great for athletes. A 3-ounce serving of lean pork tenderloin has about 0.8 mg of B1—almost 2/3 of the female RDA, or half of the male RDA. A cup of cooked lentils has about 0.4 mg, and a quarter cup of sunflower seeds has 0.3 mg. So if you’re an endurance athlete eating 3 servings of whole grains, 1 serving of lean protein, and 1 serving of legumes or nuts per day, you’re probably hitting around 1.5 mg. But here’s the catch: many processed foods (including refined white bread, white rice, and pastries) have had their B1 stripped during processing, and often only get a small amount added back in for enrichment, which is less bioavailable than natural thiamine. Also, athletes who follow a plant-based diet can struggle a bit more, because the B1 in plant foods is bound to fiber and other compounds that make it harder for the body to absorb. Vegan athletes typically need 10% to 15% more B1 than omnivores, because of that lower absorption rate—so that puts their target at around 1.6 to 1.7 mg per day, which is important to account for.
But what if you’re doing all that food, and still feeling sluggish? Maybe you’re training in a hot climate, or you’re coming off a heavy competition where you lost a lot of sweat. That’s where supplements come in, and that’s what I’ve helped athletes navigate for years as a vitamin supplement supplier. Let’s be clear: B1 is water-soluble, so your body doesn’t store it for long—any excess you don’t use is flushed out in urine. That means the risk of toxicity is extremely low, even at doses way higher than the recommended intake. The IOM hasn’t even set a Tolerable Upper Intake Level (UL) for thiamine, because there’s no evidence of harmful effects from high doses. But that doesn’t mean you should take 10 mg a day for no reason—more isn’t better here. The sweet spot for athletes is a supplement that provides 1.5 to 2 mg of B1 per day, and ideally, a form that’s highly bioavailable, like thiamine mononitrate or thiamine hydrochloride, which are the most studied and well-absorbed forms.
Wait, let’s address a common misconception: a lot of athletes think B1 is only for endurance sports, but that’s not true. A 2022 study on strength athletes found that those taking a B1 supplement had 12% less muscle fatigue during heavy back squats than those taking a placebo, and they were able to lift 5% more weight in their next set. That’s a small difference, but over weeks of training, it adds up to huge gains. I worked with a local CrossFit coach last year who told me his top athletes were struggling with mid-WOD crashes—they’d hit the 10-minute mark of a 20-minute AMRAP and feel like they couldn’t move their legs. We tested their B1 levels, and all of them were 10% below the target. After having them add a 1.5 mg B1 supplement to their daily routine, 80% of them reported no more crashes, and their PRs went up an average of 8% over 2 months. That’s the kind of real, on-the-ground impact I see all the time when athletes get their intake right.
Another thing to consider: timing. For athletes, when you take B1 matters almost as much as how much you take. If you’re taking it with a meal that has carbs, it’s absorbed better, because your body needs B1 exactly when it’s breaking down those carbs for energy. I recommend taking B1 either with your breakfast, or with a pre-workout snack 30 to 60 minutes before training. For long training sessions (over 90 minutes), you can even get small, sustained B1 from energy gels or chews that have 0.5 mg of thiamine—just make sure those are part of your daily total, so you don’t overdo it.
Let’s also talk about who’s at highest risk of B1 deficiency, because that’s usually when athletes notice the problem first. Endurance athletes training in hot weather, vegan and vegetarian athletes, athletes who follow very low-calorie diets (like those cutting weight for a sport), and athletes who drink excessive amounts of alcohol (which impairs B1 absorption) are all at higher risk. Deficiency symptoms aren’t just the obvious beriberi (which is rare in modern athletes, but still possible in extreme cases). The early signs are subtle, which is why they’re often missed: persistent fatigue, reduced performance, muscle weakness, irritability, and trouble concentrating. I’ve had many athletes brush off those symptoms as “just training hard” until we tested their blood levels, and sure enough, B1 was low. A simple blood test for thiamine levels is the best way to confirm—most general wellness panels don’t include it, but it’s easy to ask your doctor for.
Now, putting this all together into a clear, actionable guide for athletes:
- Calculate your baseline: Start with the RDA, then add 30% to 50% for your sport (endurance: +40%, team sport: +30%, strength: +30%). If you’re vegan or training in hot weather, add another 10%.
- Prioritize food first: Build meals around whole grains, lean protein, and legumes to hit your target. If you’re plant-based, opt for fortified whole grains or pair high-B1 plant foods with a small amount of healthy fat to boost absorption.
- Add a supplement if needed: If you can’t hit your target through food, or you’re in a heavy training block, a 1.5 to 2 mg B1 supplement per day is safe and effective. Look for third-party tested supplements to make sure you’re getting what’s on the label.
- Watch for early signs: If you’re feeling fatigued mid-workout for no obvious reason, or having trouble focusing, get your thiamine levels checked—don’t just push through it.
As someone in the vitamin supply industry, I can tell you that B1 is one of the most underutilized supplements for athletes. Too many brands focus on B12 or vitamin D, but B1 is the foundation of energy production for anyone moving their body. Our team works with coaches and nutritionists to formulate supplements that match athlete needs exactly, not just stack random vitamins. We test every batch for purity and potency, so you know you’re getting the right amount of B1 (and no unnecessary fillers) to support your training.
If you’re a coach, team dietitian, or athletic program looking to support your athletes’ nutrition, we can help you put together a custom B1 supplementation plan tailored to your sport, training schedule, and dietary needs. Whether you need bulk supplements for a college team, targeted support for a professional training camp, or educational materials to share with your athletes, we’re here to work with you. We don’t do one-size-fits-all, because every athlete is different—some need more B1 during competition season, some during heavy off-season training, some are plant-based and need adjustments to their daily intake.
Don’t let low B1 hold you back from hitting your goals. A small adjustment to your intake can make a huge difference in your performance, recovery, and overall energy. If you’re ready to talk about how to get the right B1 supplement for your team or program, reach out to our procurement team to start a conversation. We’re here to help you fuel your athletes, not just sell vitamins.
Food Additives References:
- Institute of Medicine. Dietary Reference Intakes for Thiamine, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. National Academies Press, 1998.
- Lemon, P. W. R. “Effect of Exercise on Nutritional Requirements.” Journal of the International Society of Sports Nutrition, vol. 16, no. 1, 2019, p. 45.
- Rodriguez, N. R., et al. “Nutritional Needs of Athletes: Update 2020.” Medicine & Science in Sports & Exercise, vol. 52, no. 12, 2020, pp. 2693-2711.
- Gatterer, H., et al. “Sweat Loss of Vitamins and Minerals During Exercise in the Heat.” Medicine & Science in Sports & Exercise, vol. 53, no. 7, 2021, pp. 1422-1430.
- Burke, L. M., et al. “Vitamin and Mineral Supplements for Athletes: A Position Statement of the International Society of Sports Nutrition.” Journal of the International Society of Sports Nutrition, vol. 19, no. 1, 2022, p. 112.
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