The creatine scoop — essential cautions for the kidney community

You've probably heard of creatine, a dietary supplement heavily promoted by health influencers as a way to increase muscle mass and potentially improve brain health. A recent report found that sales of the supplement have soared past $500 million in the U.S. 

So, what is creatine? Is it worth the hype? Does it come with risks? And do the answers to these questions change if you have kidney disease?

We asked Jing Feng of AKF's Dietitian Advisory Group to help us better understand this supplement craze. Jing is a registered dietitian who provides comprehensive nutrition care to in-center dialysis patients.

What is creatine? What does it do for your body?

Creatine is a natural compound made in your body. It is found naturally in animal products, such as beef, poultry and fish. It also helps your muscles tighten quickly and powerfully. This can make sprinting or lifting heavy weights easier.

How do you get it in your diet without taking a supplement? 

You can get it from your diet. But your body also makes it naturally. A regular diet that does not exclude animal products usually gives you about 1 to 2 grams of it a day. 

Think of your muscles like a fuel tank for creatine. The amount you get from a regular non-vegetarian diet only fills that tank about 60%-80% of the way. If you follow a vegetarian diet, you have a lower baseline and start with a tank that is only about half-full. 

Why do people take creatine as a supplement? What are the benefits? 

Many athletes and weightlifters take a supplement called creatine monohydrate to fill their muscle fuel tanks close to 100%. Taking this supplement can help you jump higher, run faster and lift heavier weights. There's also increasing interest in taking these supplements to promote healthy aging.

But keep in mind: it doesn't work for everyone. Some people won't notice any difference at all if their muscle fuel tank is already at 100%. Everyone responds differently to creatine.

How does it work? Is it bad for your kidneys?

Your muscles rely on a molecule called ATP (adenosine triphosphate) to fuel you when you exercise. Think of ATP as a fully charged battery with three little energy parts called phosphates attached to it. Every time you eat, your body acts like a factory, breaking down your food to recharge these tiny ATP batteries.

Your muscles only hold enough fully charged ATP to last for a few seconds of hard exercise. That is where creatine comes in. It carries spare phosphate parts and when you take a supplement, it instantly plugs them back into your drained batteries, turning them back into fresh ATP. This helps maintain a continuous energy supply so you can keep running or lifting during intense training.

Many people worry that taking creatine might hurt their kidneys. However, for generally healthy people without any kidney problems, studies have not shown that taking a standard dose (less than 5 grams per day) could hurt the kidney function. Even so, you should always check with your doctor before starting any new supplements. 

What's the difference between creatine and creatinine? Can creatine supplements change kidney lab results, such as creatinine levels? 

Though they confusingly look similar on paper, creatine and creatinine are two completely different concepts. 

Creatine provides the functional energy your muscles need to contract and perform physical activities. 

Creatinine, on the other hand, is a waste product of muscle creatine metabolizing that cannot be recycled back into energy. Instead, it enters the bloodstream and is filtered out by the kidneys into your urine. 

Because of this relationship, creatine supplements can raise your serum creatinine levels. However, this change does not affect your actual glomerular filtration rate (GFR) and does not mean your kidney function is impaired.

What are the risks of taking a creatine supplement? Who should be careful?

Currently, we don't have enough data about the safety or risks of kidney patients taking it as a supplement to definitively say. 

People with pre-existing kidney conditions, such as  chronic kidney disease or any other conditions that may impair kidney function like high blood pressure, diabetes or heart disease, should talk to their doctors before taking any supplements. Your doctor can then help prevent any potential complications. 

As mentioned earlier, taking creatine can elevate creatinine. People with pre-existing kidney conditions can be overwhelmed by creatine, potentially damaging the kidney further because the organ needs to work harder to filter out the creatinine.  

What should I know before taking creatine, or any other supplements?

Look for a seal on the container from an independent testing organization, such as NSF Certified for Sport, Informed-Choice/Informed-Sport, USP (United States Pharmacopeia) or ConsumerLab.com. These third parties verify that what is listed on the label is what is inside the bottle. 

If you are thinking of starting a new supplement, it is important to know your baseline lab numbers. Getting routine blood work — including kidney function tests like serum creatinine and eGFR — can help you understand exactly how your body responds to the supplement over time. Since everyone responds to supplements differently, it's important to discuss your plans with your doctor to ensure it is safe for you to take. 

If you currently take any medicines, your provider can also check to see if a new supplement could cause your medicines to work differently.

Is there an ideal or normal range of creatine to have in your body? If so, how can you tell if your body has too much or too little?

An average person who weighs about 155 pounds (70 kg) holds roughly 120 grams of creatine inside their muscles. Every day, the body naturally burns through and replaces about 1% or 2% of that total pool. 

If you overload your system by taking too much of the supplement, your body has to work overtime to break down the extra amount. This will temporarily spike the amount of waste in your blood as your body tries to clear out the excess. Consuming too much at once can also cause side effects like stomach cramping or diarrhea and temporary weight gain from water being pulled into the muscle cells.

On the other hand, people with lower overall muscle mass typically maintain smaller total creatine stores. They often have lower baseline serum creatinine levels and may experience premature fatigue during strenuous, high-intensity physical activities. This is most common in people dealing with severe nutritional deficiencies, sarcopenia (muscle wasting) or malnutrition.

Are there any common misconceptions about creatine and kidney function that you'd like to clear up?

A widespread misconception is that it causes dehydration. Yes, it does draw water directly into your muscle cells. But it does not deplete the rest of your body of necessary fluids or increase your risk of dehydration. 

Additionally, keeping muscle tissue well-hydrated can actually provide a protective effect against cramping and heat illness when training in hot temperatures.

Final takeaway: What's the most important thing people should know about creatine and kidney health before starting a supplement?

Because creatine supplementation naturally elevates your serum creatinine levels, it's important to inform your doctor prior to any routine blood work. This allows your doctor to accurately interpret your metabolic panels and avoid any unnecessary misinterpretation of your true kidney health. 

And as I mentioned earlier, it's important to talk to your doctor about any supplements you want to use before you begin taking them.

Jing Feng, MSPH, RDN is a registered dietitian who earned her Bachelor of Science in nutritional sciences from Cornell University and a Master of Science in public health from the Johns Hopkins Bloomberg School of Public Health. She currently works as a renal dietitian, providing comprehensive nutrition care to in-center dialysis patients.

In addition to serving on AKF's Dietitian Advisory Group, she is an active member of the National Kidney Foundation and the Academy of Nutrition and Dietetics.