ZMA, a nutritional supplement, is lauded by bodybuilders to increase muscle mass and strength, improve sleep and immune function, and even increase testosterone levels. However, scientific research supports only a fraction of these claims and warns about important drawbacks. Read on to learn more about ZMA benefits, side effects, and interactions.
What Is ZMA?
ZMA, or Zinc Magnesium Aspartate, is a nutritional supplement that contains zinc monomethionine aspartate, magnesium aspartate, and vitamin B6 [1].
Zinc is a trace element, meaning it is only needed in small amounts in the body but is essential for humans. Magnesium is an essential macroelement (needed in relatively large amounts). Vitamin B6 may increase the effect of zinc and magnesium and deliver additional benefits on energy production [2, 3, 4].
Many have claimed that ZMA is necessary for bodybuilding and exercise because some evidence suggests that athletes are deficient in zinc and magnesium due to increased exertion. However, other studies found the opposite to be true, while a review found mixed results [5, 6, 7, 8, 9, 10, 11, 1, 12, 13, 14].
Zinc and magnesium deficiencies are also linked to other conditions, such as ADHD, stress/anxiety, and reduced immune function [15, 16, 17].
Snapshot
Proponents:
- May improve athletic performance
- May relieve stress and fatigue
- Supports the immune system
- May help with ADHD
Skeptics:
- Solid clinical evidence is lacking
- Supportive research may be biased
- Excess amounts may cause digestive side effects
- May interact with a range of prescription drugs
How It Works
As ZMA is a nutritional supplement, it works by providing the body with adequate (or excess) levels of zinc, magnesium, and vitamin B6 for proper functioning. As the body does not store zinc, it must be replenished via diet [18, 1, 19].
ZMA contains: about 3 times the recommended daily dose of zinc (30 mg); about the recommended daily dose of magnesium for adult men (450 mg); about 10 times the recommended daily dose of vitamin B6 (11 mg) [18, 1, 20, 21].
While some claim that this ratio in ZMA is important for its action, there are no studies to support the claims.
Potential Health Benefits of ZMA
We base most of the health benefits of ZMA solely on comparable studies about each of its components, due to lack of other data. Studies with ZMA exist only for the first two benefits listed.
Insufficient Evidence:
No valid clinical evidence supports the use of ZMA for any of the conditions in this section. Below is a summary of up-to-date animal studies, cell-based research, or low-quality clinical trials which should spark further investigation. However, you shouldn’t interpret them as supportive of any health benefit.
1) Athletic Performance and Strength
Interestingly, one of the few studies that tested the effects of all 3 components as the ZMA supplement found no significant changes in hormones, body composition, bench press and leg press, upper- or lower-body muscular endurance, or cycling breathing performance in 42 trained men [1].
In a study with 23 triathletes, magnesium supplementation increased swimming, cycling, and running speed. Zinc levels in the blood were correlated with increased athletic performance in 21 football players (as measured by an exercise test on a cyclo-ergometer machine and blood lactate levels) [22, 23].
A study of 30 healthy adults found that magnesium supplementation and martial arts together increased 2 types of red blood cells, which may help with athletic performance. This same effect was seen with zinc [24, 25, 26].
In 26 healthy untrained adults, magnesium supplementation greatly increased strength. Another study of 8 healthy men showed low zinc decreases knee and shoulder muscle capacity. Zinc supplementation increased strength in 16 healthy women [27, 28, 29].
Despite some positive results for individual components, there’s insufficient evidence to support the use of ZMA for improving athletic performance and strength.
2) Testosterone Levels
One study found ZMA supplementation increased testosterone levels of 27 healthy football players without nutritional deficiencies [30].
However, ZMA supplementation (30 mg zinc, 450 mg magnesium, and 11 mg vitamin B6) did not affect testosterone levels in the blood of 14 healthy men without nutritional deficiencies. Another study with ZMA found no significant changes in hormones in 42 healthy trained men [31, 1].
In infertile men (with low blood testosterone), supplemental zinc led to an increase in sperm count, testosterone, dihydrotestosterone (DHT), and fertility [32].
In infertile men (with low blood testosterone), supplemental zinc led to an increase in sperm count, testosterone, dihydrotestosterone (DHT), and fertility [32].
Zinc deficiency resulted in lower levels of testosterone in the blood in rats. The rats fed a zinc-deficient diet were also more sensitive to estrogen (more receptors for female sex hormones) and less to androgens (fewer receptors for male sex hormones) [33, 34].
Zinc supplementation, in general, may help restore testosterone levels, while the evidence for ZMA is less convincing.
3) ADHD
ADHD is a disorder characterized by inattention and hyperactivity. Two reviews suggested that ADHD in children is associated with nutritional deficiency, such as zinc and magnesium [15, 35].
Supplemental levels of zinc (15 mg, twice a day) improved response to ADHD medication in children (52 participants). In another study of children with ADHD, zinc (150 mg/day) improved hyperactive, impulsive, and impaired-socialization symptoms but had no effect on attention deficit symptoms (400 participants) [36, 37].
A large study found that magnesium, zinc, and polyunsaturated fatty acids curbed both attention deficit and hyperactivity issues in 810 children. The combination of magnesium with vitamin B6 was effective in another study of 76 children with ADHD [38, 3].
4) Immunity
In a study with 153 children, treatment with zinc (10 mg/twice a day) shortened the duration of fever in boys (but not girls) with a severe lower respiratory infection. Zinc supplementation (10 mg/day) also reduced the frequency of respiratory infections over a period of 6 months in a study with 609 children [39, 40].
A review study on micronutrients identified zinc and vitamin B6 (among a few other nutrients) as important to immune function. This may justify the combination of ZMA [41].
In clinical states associated with immunodeficiency (e.g., sickle cell disease, human immunodeficiency virus (HIV) infection) and in the elderly, zinc supplementation can restore natural killer cell activity, lymphocyte production, and resistance to infections [42, 43, 44, 45].
Vitamin B6 deficiency slowed white blood cell production in mice, pointing to its role in maintaining a healthy immune system [46].
5) Stress
Magnesium supplementation prevented increases in the stress hormone, cortisol, and in another hormone, aldosterone, following exercise in nine healthy men. Similarly, zinc given to medical students reduced the release of the stress hormone, cortisol. In a study with 54 individuals, those with anxiety had lower levels of zinc in their blood compared to controls [47, 48, 16].
In a study with 23 triathletes, magnesium supplementation lowered serum cortisol levels, a measurement of stress [22].
A specific multivitamin that contains magnesium and B6 reduced stress levels and increased mood in 60 healthy adult workers [49].
These studies may justify the combination in ZMA, but more evidence is needed.
6) Fatigue
Zinc prevented exercise-induced fatigue (measured as a drop in thyroid hormone and testosterone levels) in a study of 10 sedentary men. The same result was seen in 10 male wrestlers. Similarly, magnesium supplementation prevented a drop in TSH levels triggered by exhaustion during martial arts training [50, 51, 52].
One study found that blood zinc levels were significantly lower in chronic fatigue syndrome (CFS) patients and that symptom severity was negatively correlated with blood zinc levels. The study concluded that zinc may be effective in attenuating CFS symptoms because of its antioxidant and anti-inflammatory properties [53].
A study found that treating leaky gut with a mixture of anti-inflammatory and antioxidant substances including zinc in CFS patients resulted in a significant improvement of symptoms [54].
Limitations and Caveats
While there are quite a few studies of the effects of both zinc and magnesium on humans, there is not much data on zinc, magnesium, and vitamin B6 together.
The main paper referenced by many bodybuilding sources claims that ZMA increased testosterone levels and strength in a study with 27 football players. However, one of the authors owns the company that makes the specific ZMA formulation. The same company funded the research [30].
This points to a massive conflict of interest and makes the results questionable.
Two other studies also looked at the effects of ZMA and did not see changes in testosterone levels or strength (14 and 42 healthy men respectively) [1, 31].
ZMA Side Effects & Precautions
This list does not cover all possible side effects. Contact your doctor or pharmacist if you notice any other side effects. In the US, you may report side effects to the FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch. In Canada, you may report side effects to Health Canada at 1-866-234-2345.
An excess dose of zinc can cause nausea, vomiting, stomach pain, sluggishness (lethargy), and extreme tiredness (fatigue). Even taking a non-toxic dose of 100 to 300 mg of zinc a day can cause copper deficiency with symptoms of anemia, low white blood cells (neutropenia), and reduced immune function [55].
Although rare, it is possible to overdose on magnesium (hypermagnesemia), which can cause abdominal cramping, diarrhea, and nausea [56, 57, 58, 59].
High doses of vitamin B6 can cause neurological effects, skin lesions, sensitivity to light, nausea, and heartburn [60, 61].
That said, the amounts of zinc, magnesium, and B6 present in ZMA are safe and well-tolerated for most healthy people.
Interactions
Supplement-drug interactions can be dangerous and, in rare cases, even life-threatening. Always consult your doctor before supplementing and let them know about all drugs and supplements you are using or considering.
ZMA can interact with a variety of other drugs and other supplements because it is composed of zinc, magnesium, and vitamin B6.
Zinc can interfere with copper and iron usage in the body. It also interacts with the following drugs [55, 62, 63, 64, 65, 66]:
- Antibiotics: Quinolone and tetracycline antibiotics interact with zinc in the stomach and intestines and prevent the body from absorbing both zinc and the antibiotic
- Penicillamine: Zinc interacts with penicillamine, preventing the body from absorbing it
- Diuretics: Thiazide diuretics cause the body to evacuate zinc in urine
Magnesium interacts with a variety of drugs [67, 68, 69, 70, 71]:
- Bisphosphonates used for the treatment of osteoporosis: Magnesium prevents the body from absorbing this drug
- Antibiotics: Tetracyclines and quinolone antibiotics can form complexes with magnesium
- Diuretics: Loop, thiazide, and ethacrynic acid diuretics cause the body to evacuate magnesium in urine while potassium-sparing diuretics do the opposite
- Proton pump inhibitors, used for acid reflux (GERD): PPIs taken for over a year can cause magnesium deficiency but the exact mechanism is not known
Vitamin B6 interacts with the following drugs [60, 72, 73, 74]:
- Cycloserine: This antibiotic causes the body to evacuate vitamin B6 in urine
- Anti-seizure medications: Valproic acid, carbamazepine, and phenytoin cause the body to break down vitamin B6, potentially resulting in a deficiency
- Theophylline: This drug may cause a vitamin B6 deficiency, though the mechanism is unknown
Supplementing With ZMA
ZMA supplements have not been approved by the FDA for medical use. In general, regulatory bodies aren’t assuring the quality, safety, and efficacy of supplements. Speak with your doctor before supplementing.
ZMA supplements are widely available, almost exclusively in pill form, but are also found in powder form. ZMA is available by itself or mixed with other substances meant to encourage muscle development, recovery, or sleep, such as theanine and 5-HTP (5-Hydroxytryptophan).
Dosage
The below doses may not apply to you personally. If your doctor suggests using ZMA, work with them to find the optimal dosage according to your health condition and other factors.
The only three specific ZMA studies (change in testosterone levels and athletic performance and no changes) used a dosage of ZMA equivalent to [30, 1]:
- 30 mg zinc monomethionine aspartate
- 450 mg magnesium aspartate
- 11 mg vitamin B6
User Reviews
The opinions expressed in this section are solely from the users who may or may not have a medical background. SelfDecode does not endorse any specific product, service, or treatment. Do not consider user experiences as medical advice. Never delay or disregard seeking professional medical advice because of something you have read on SelfDecode.
One user reported a combination of ZMA and melatonin greatly improved sleep quality. Similarly, another user said it helped his muscles relax for better sleep. A third user said it improved sleep duration.
A few users didn’t see any results.
One user said it improved their migraines and attributed it to the magnesium.
