Magnesium is an important mineral that many people don’t get enough of, and regular magnesium supplements don’t work as well as they could. Scientists tested two different types of magnesium that come from seawater to see which one your body absorbs better. They gave 20 healthy young adults either a placebo, magnesium citrate, or magnesium hydroxide—all containing the same amount of actual magnesium. Both seawater magnesium types worked much better than the placebo, but they worked about equally well. The hydroxide version might be slightly better because you need to swallow fewer pills to get the same amount of magnesium.

The Quick Take

  • What they studied: Whether two different ways of processing magnesium from seawater result in different amounts of magnesium your body actually uses
  • Who participated: 20 healthy young men and women who completed the study three separate times, testing each type of magnesium plus a fake pill
  • Key finding: Both seawater magnesium types helped your body absorb more than 97% more magnesium compared to the placebo, but they worked about the same as each other when the doses were equal
  • What it means for you: If you need a magnesium supplement, seawater-derived magnesium appears to work better than traditional sources. The hydroxide form might be slightly more convenient since you’d take fewer pills, though both types are effective. Talk to your doctor before starting any supplement.

The Research Details

This was a carefully controlled experiment where 20 healthy young adults came back three different times to test three different substances: a fake pill (placebo), seawater magnesium citrate, and seawater magnesium hydroxide. The researchers used a “crossover” design, meaning each person tried all three options at different times. Nobody—not the participants or the researchers giving out the pills—knew which substance was which until the study ended. This helps prevent bias from affecting the results.

To measure how well each magnesium type worked, the scientists collected urine from participants over 18 hours after they took each substance. They also checked blood magnesium levels at 1 and 2 hours after taking the pills. All the magnesium doses were set to match the official daily recommendation for magnesium, so the comparison would be fair. The researchers measured magnesium levels three times each to make sure their results were accurate.

Using urine collection over 18 hours is a reliable way to measure how much magnesium your body actually absorbed and used, rather than just measuring what you swallowed. By testing each person with all three options, the researchers could fairly compare the two seawater magnesium types without differences between people getting in the way. The double-blind design (where nobody knew which pill was which) prevents expectations from influencing the results.

This study has several strengths: it used a double-blind design to prevent bias, tested each person multiple times for accuracy, and measured magnesium in multiple ways (urine and blood). However, the sample size of 20 people is relatively small, and all participants were young and healthy, so results might not apply to older adults or people with health conditions. The study was published in a peer-reviewed journal, meaning other experts reviewed it before publication.

What the Results Show

Both seawater magnesium preparations dramatically outperformed the placebo, with participants absorbing more than 97% additional magnesium compared to the fake pill. This is a huge difference and shows that seawater magnesium works very well. When the researchers compared the two seawater magnesium types directly to each other—making sure the actual magnesium content was equal—they found no meaningful difference in how much magnesium the body absorbed. Both the citrate form and the hydroxide form worked equally well.

The magnesium hydroxide version contained more actual magnesium per pill (at least 33%) compared to the citrate version (at least 10%). This means you’d need to take fewer pills of the hydroxide form to get the same amount of magnesium. For people who don’t like taking lots of pills, this could be an advantage, even though both forms work equally well.

The blood magnesium measurements taken at 1 and 2 hours after taking the supplements confirmed what the urine tests showed—both seawater magnesium types were being absorbed effectively. This double-checking method strengthens confidence in the results. The fact that both forms worked so much better than placebo suggests that the seawater source itself, with its mix of 72 different minerals, may help magnesium absorption better than traditional magnesium supplements.

Earlier research had already shown that seawater-derived magnesium works better than traditional magnesium sources. This new study confirms that finding and adds important information: it shows that two different ways of processing seawater magnesium work about equally well. This helps narrow down which type might be best for different situations—the hydroxide form for convenience, or either form if you prefer.

The study only included 20 people, all of whom were young and healthy. We don’t know if these results would apply to older adults, children, or people with health conditions or digestive problems. The study was relatively short-term, so we don’t know about long-term effects of taking these supplements. Additionally, the study was funded by the company that makes these magnesium products, which could potentially influence results, though the double-blind design helps reduce this risk.

The Bottom Line

If you need a magnesium supplement, seawater-derived magnesium appears to be a good choice based on this research (moderate confidence level). It seems to work much better than traditional magnesium supplements. Between the two types tested, either the citrate or hydroxide form should work well—choose based on convenience (fewer pills with hydroxide) or personal preference. Always consult your doctor before starting any supplement, especially if you take medications or have kidney problems.

People who have been told they have low magnesium, those interested in improving their magnesium intake, and anyone currently taking magnesium supplements who wants to know if a better option exists should pay attention to this research. People with kidney disease should NOT start magnesium supplements without doctor approval. Young, healthy people without magnesium deficiency may not need supplements at all.

Magnesium absorption happens relatively quickly—the study showed measurable increases in blood magnesium within 1-2 hours. However, health benefits from improved magnesium levels typically take weeks to months to notice, depending on what symptoms you’re trying to address. Be patient and consistent with supplementation.

Want to Apply This Research?

  • Track daily magnesium supplement intake (type and dose) and note any changes in energy levels, sleep quality, or muscle tension over 4-8 weeks. Record the specific product name (citrate vs. hydroxide) to identify which works better for you personally.
  • If currently taking traditional magnesium supplements, consider switching to a seawater-derived magnesium product (after consulting your doctor). If using the citrate form, you might experiment with the hydroxide form to reduce pill burden while maintaining the same magnesium dose.
  • Set a daily reminder to take your magnesium supplement at the same time each day. Monthly, review your tracked symptoms and energy levels to assess whether the supplement is helping. If switching between citrate and hydroxide forms, track for at least 2-3 weeks with each to notice any personal differences in how you feel.

This research summary is for educational purposes only and should not replace professional medical advice. Before starting any magnesium supplement, consult with your healthcare provider, especially if you have kidney disease, heart conditions, or take medications. This study involved only 20 healthy young adults, so results may not apply to everyone. The study was relatively short-term, and long-term effects are not established. Always inform your doctor about supplements you’re taking, as they can interact with medications.