In brief. Magnesium contributes to normal muscle function, normal functioning of the nervous system, normal energy-yielding metabolism, and the reduction of tiredness and fatigue. Intake may fall short because of a limited diet, certain circumstances, and increased needs. Only a doctor can diagnose a deficiency, and a standard blood test has limitations because most magnesium is stored in cells and bones. A balanced diet comes first; a supplement contains a measured amount of magnesium per serving. This is information, not medical advice.
What does magnesium do in the body?
Magnesium is an essential mineral that the body cannot produce, so it must come from food or supplements. The authorised claims state that magnesium contributes to normal muscle function, to normal functioning of the nervous system, to normal energy-yielding metabolism, to a reduction of tiredness and fatigue, to normal protein synthesis, to normal psychological function, to electrolyte balance, and to the maintenance of normal bones and teeth. Magnesium also has a role in the process of cell division. These are the permitted ways to describe magnesium, and they apply to the mineral itself.
Why might magnesium intake fall short?
For most healthy people, a varied diet meets their magnesium needs. Even so, intake may fall short for several reasons. A limited diet low in vegetables, whole grains, nuts, and pulses provides less magnesium. Highly processed foods and refined grains contain less than their whole-grain equivalents. Periods of stress, intense physical activity, and heavy sweating can increase the amount the body uses or loses. Older adults sometimes eat less and absorb nutrients less efficiently, while people who drink little and eat a mineral-poor diet may take in less. Differences between people can be real, and needs can vary by situation. None of this is the same as a diagnosed deficiency; it only explains why the gap between intake and need may grow.
Who is more likely to have a low magnesium intake?
Some groups are more likely to have a lower intake or greater needs. The amounts the body needs can also vary. The list below is for information and does not replace a medical assessment.
- People with a limited or restrictive diet, low in vegetables, whole grains, nuts, and pulses.
- Older adults, who may eat smaller portions and absorb minerals less efficiently.
- People under prolonged stress or doing intense physical activity, who may use or lose more.
- People with certain digestive or kidney conditions, or those taking specific medicines, whose mineral status is monitored by a doctor.
- Pregnant or breastfeeding women, who have greater needs and should follow medical advice.
Belonging to one of these groups does not mean you have a deficiency. It is a reason to pay attention to your diet and, if you have concerns, speak to a doctor.
Why do people have their magnesium levels checked?
People often ask about magnesium when they feel persistently tired, notice that their diet has become limited, or simply wonder whether they are getting enough. A doctor may decide to check magnesium as part of a broader assessment, especially when there are specific medical reasons. It is important to be honest here: everyday concerns such as tiredness have many possible causes and are not evidence of magnesium deficiency. A qualified professional looks at the whole picture rather than a single sign.
Why does a magnesium blood test have limitations?
Only a small proportion of the body's magnesium circulates in the blood. Most is stored in cells and bones, which means that a standard blood test, serum magnesium, can be within the normal range even when overall stores are lower. That is why a doctor does not rely on a single number, and why you cannot diagnose a deficiency yourself. If a deficiency is suspected, a doctor will decide which tests are appropriate and interpret them alongside your diet, health, and any medicines you take.
Which foods are rich in magnesium?
A varied diet is the most reliable foundation for magnesium intake. The foods below are widely recognised as good sources.
| Food group | Examples | Note (for information) |
|---|---|---|
| Whole grains | Wholemeal bread, oats, brown rice | Whole-grain versions contain more than refined grains |
| Nuts and seeds | Almonds, cashews, pumpkin seeds | Concentrated sources that work well in small portions |
| Pulses | Beans, lentils, chickpeas | Pair well with whole grains in everyday meals |
| Green vegetables | Spinach, kale, other leafy greens | Leafy greens are a classic plant source |
| Other foods | Dark chocolate, bananas | Contribute alongside the groups above |
No single food needs to take centre stage; building meals around these groups is the simplest way to support a normal dietary magnesium intake.
Where does a magnesium supplement fit in?
A supplement is intended to complement a varied diet, not replace it. When dietary intake may fall short, a magnesium supplement can help support a normal intake, and through the mineral itself, magnesium contributes to normal muscle function, normal functioning of the nervous system, and the reduction of tiredness and fatigue. Magnesium comes in different forms that vary mainly in solubility and tolerability, and no single form is right for everyone; we explain this in our article about the forms of magnesium. A supplement does not diagnose or address a condition; it simply adds to your intake within the recommended dosage.
Is magnesium safe?
Magnesium from food and supplements is generally well tolerated by healthy adults at normal doses. The most common side effect of higher supplemental doses is a laxative effect, such as loose stools or diarrhoea, which occurs more often with readily soluble forms. People with impaired kidney function should be cautious because the kidneys remove excess magnesium. Do not take more magnesium than the recommended dosage without advice. If you are pregnant or breastfeeding, take medicines, including certain antibiotics or heart or blood pressure medicines, or have a kidney condition, speak to a doctor or pharmacist first. A supplement is not a substitute for a varied diet or medical care, and persistent concerns should always be discussed with a doctor.
Frequently asked questions
What are common reasons for magnesium intake to fall short?
A limited diet low in vegetables, whole grains, nuts, and pulses, a high intake of processed foods, and circumstances such as prolonged stress, intense physical activity, or heavy sweating can widen the gap between intake and need. Older adults may also eat less and absorb less efficiently, and needs can genuinely vary between people. These are reasons why intake may fall short, not a diagnosis.
Can I diagnose a magnesium deficiency myself?
No. A deficiency is diagnosed by a doctor, who considers your diet, health, medicines, and appropriate tests together. Everyday concerns such as tiredness have many causes and are not evidence of low magnesium. If you are concerned, speak to a qualified professional.
Why is a magnesium blood test not enough on its own?
Most magnesium is stored in cells and bones, while only a small proportion circulates in the blood. A standard serum test can therefore be normal even when overall stores are lower, so a doctor interprets it alongside other information rather than relying on a single value.
Which foods can help me get enough magnesium?
Whole grains, nuts and seeds, pulses, green leafy vegetables, and foods such as dark chocolate and bananas are widely recognised as sources. Building varied meals around these groups is the most reliable way to support a normal dietary intake.
Should I take a magnesium supplement?
A varied diet comes first. If your dietary intake may fall short, check the label and recommended dosage before choosing a magnesium supplement. A supplement complements rather than replaces your diet; if you take medicines, have a condition, or are pregnant or breastfeeding, ask a doctor or pharmacist for advice first.
Sources
- EU Register of nutrition and health claims made on foods (permitted claims for magnesium). Commission Regulation (EU) No 432/2012. ec.europa.eu
- Regulation (EC) No 1924/2006 on nutrition and health claims made on foods.
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific opinions on the substantiation of health claims related to magnesium. EFSA Journal. 2009 and 2010.
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific opinion on dietary reference values for magnesium. EFSA Journal. 2015;13(7):4186.
Written by the NOTFORTOMORROW editorial team. How we research: we base factual statements on the official EU Register of health claims and peer-reviewed sources, cite our sources, and date our reviews. This article is for information, not medical advice; speak to a qualified professional about your situation. Last reviewed: 2026-06-06.
