Leucine Supplement Side Effects

Most Americans easily get enough leucine from foods rich in this essential amino acid. Such foods include poultry, fish, meat, nuts, seeds and dairy products like yogurt and cottage cheese. Leucine supplements may increase athletic performance and muscle strength, says the Memorial Sloan Kettering Cancer Center, though more research is needed. While you can't consume enough leucine from foods to cause harmful side effects, you should use leucine supplements with caution.

Recommended Intake and Sources

Healthy adults need approximately 42 milligrams of leucine per kilogram of their body weight each day. An average man weighing 196 pounds would require about 3,733 milligrams of leucine daily, while a woman of 166.2 pounds should have around 3,166 milligrams. To avoid the possible side effects of leucine supplements, it's best to obtain the majority of the amino acid through diet. Excellent sources include turkey breast, which contains 2,076 milligrams in every 3-ounce serving, and roasted soybeans, with nearly 5,000 milligrams per cup.

Effect on B Vitamins

Leucine Overdose

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In 2012, a study published in the "Journal of Nutrition" reported that men taking more than 39 grams, or 39,000 milligrams, of supplemental leucine per day had an increased likelihood of experiencing harmful side effects. One of these side effects can include vitamin B-3 and vitamin B-6 deficiency since leucine interferes with the body's ability to synthesize these nutrients. Not having enough vitamin B-3 -- also known as niacin -- may cause vomiting, depression and indigestion and may increase your risk of Alzheimer's disease and high blood cholesterol. A lack of vitamin B-6, or pyridoxine, can result in memory loss, irritability and depression.

Possible Impact on the Prostate

Prostate cancer cells need leucine to grow, multiply and spread, determined a "Journal of the National Cancer Institute" study published in 2013. Leucine is delivered to these cells in the body by L-type amino acid transporters. The researchers concluded that finding a way to inhibit these transporters could prevent prostate cancer cell growth by limiting the amount of available leucine. It is not known if taking supplemental leucine and significantly increasing the amount of available leucine in the body could increase your risk of prostate cancer or speed the growth of tumors in men, however.

Interaction with Diabetes Medications

What Is the Difference Between L-Carnitine & Acetyl-L-Carnitine?

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When supplemental leucine is consumed with a source of glucose, it increases the amount of insulin your body produces and lowers your blood sugar level. Taking leucine at the same time as a diabetes medication, including insulin, may cause your blood sugar to drop too low. If you suffer from hypoglycemia -- chronic low blood sugar -- due to a medical problem or a deficiency in an enzyme or hormone, avoid taking supplemental leucine.