How much magnesium per day for a woman is a common nutritional question with important health implications. In the UK, the Reference Nutrient Intake (RNI) for adult women is 270 mg daily, rising to 320 mg during breastfeeding. Magnesium supports over 300 enzymatic reactions, contributing to energy production, bone health, cardiovascular function, and nervous system regulation. Whilst most women can meet these requirements through a balanced diet rich in green leafy vegetables, nuts, seeds, whole grains, and legumes, certain groups—including those with gastrointestinal disorders, diabetes, or taking specific medications—may face increased deficiency risk. Understanding your magnesium needs and recognising signs of inadequacy helps ensure optimal health throughout different life stages.

Recommended Daily Magnesium Intake for Women in the UK

The UK Department of Health and Social Care establishes Reference Nutrient Intakes (RNIs) for magnesium, which represent the amount sufficient to meet the needs of approximately 97.5% of the population. For adult women aged 19 and over, the RNI is 270 mg per day. This recommendation comes from the Committee on Medical Aspects of Food Policy (COMA) and continues to inform nutritional guidance across the UK.

These values differ slightly from international recommendations. The European Food Safety Authority (EFSA) suggests an Adequate Intake (AI) of 300 mg daily for adult women, whilst the US Institute of Medicine recommends 310–320 mg for younger women and 320 mg for those over 30. The UK figure of 270 mg represents an evidence-based estimate that accounts for typical dietary patterns and absorption rates in the British population.

It is important to note that these recommendations aim to ensure nutritional adequacy for the vast majority of healthy women. Individual requirements may vary based on factors including age, activity level, overall health status, and the presence of certain medical conditions.

The RNI applies to magnesium obtained through diet and, where necessary, supplementation combined. The NHS emphasises that most people should be able to obtain adequate magnesium through a balanced, varied diet rich in whole foods. However, the National Diet and Nutrition Survey (NDNS) indicates that some UK women may not consistently meet these recommendations through food alone, highlighting the importance of dietary awareness.

Why Women Need Magnesium: Key Health Benefits

Magnesium serves as a cofactor in over 300 enzymatic reactions throughout the body, making it essential for numerous physiological processes particularly relevant to women's health. This mineral plays a critical role in energy metabolism, converting food into usable energy at the cellular level through its involvement in ATP (adenosine triphosphate) synthesis.

Bone health represents another crucial area where magnesium proves vital for women. Approximately 60% of the body's magnesium resides in bone tissue, where it contributes to bone density and structural integrity. Magnesium works synergistically with calcium and vitamin D to maintain skeletal health, which becomes increasingly important for women approaching and beyond menopause when osteoporosis risk rises. Research suggests an association between adequate magnesium intake and higher bone mineral density.

Magnesium also supports cardiovascular function by helping to regulate heart rhythm, maintain healthy blood pressure, and support vascular tone. Observational studies have found associations between magnesium intake and cardiovascular health, though causality has not been established. The mineral helps regulate calcium channels in cells, contributing to blood vessel function and circulation.

Additionally, magnesium influences nervous system function and mood regulation. It modulates neurotransmitter activity and helps regulate the hypothalamic-pituitary-adrenal (HPA) axis, which governs stress responses. Some women report improvements in premenstrual symptoms when magnesium levels are adequate, though the evidence remains limited. There is also preliminary research, though not conclusive, examining potential associations between magnesium status and sleep quality or migraine frequency—both concerns that disproportionately affect women. UK clinical guidelines do not currently recommend routine magnesium supplementation for these conditions.

Magnesium Requirements During Pregnancy and Breastfeeding

Magnesium requirements change during pregnancy and lactation to support both maternal health and foetal development. The UK RNI for pregnant women remains at 270 mg per day—the same as for non-pregnant adults—as established by the Department of Health. The EFSA suggests an Adequate Intake of 300 mg daily for adult women, with no specific increase during pregnancy.

During pregnancy, magnesium supports crucial processes including foetal skeletal development, protein synthesis, and cellular energy production. Some observational studies have examined associations between magnesium status and pregnancy outcomes, though evidence remains mixed. It's important to note that routine magnesium supplementation is not recommended for all pregnant women in the UK, though adequate dietary intake remains important.

For breastfeeding women, the UK RNI increases to 320 mg per day to account for magnesium secreted in breast milk and the metabolic demands of lactation. Breast milk magnesium content remains relatively stable regardless of maternal intake, as the body prioritises infant nutrition, potentially depleting maternal stores if dietary intake proves insufficient.

Pregnant and breastfeeding women should prioritise magnesium-rich foods and discuss supplementation with their midwife or GP if concerned about their intake. Any supplementation during pregnancy should occur under medical supervision. The NHS advises that most nutrients should come from a balanced diet during pregnancy, with specific supplements (folic acid, vitamin D) recommended for all pregnant women.

Signs You May Need More Magnesium

Magnesium deficiency, termed hypomagnesaemia when clinically significant (typically defined as serum magnesium below 0.7 mmol/L), can be challenging to identify as symptoms often prove non-specific and may develop gradually. Early signs frequently include muscle cramps (particularly nocturnal leg cramps), muscle twitches or fasciculations, and generalised fatigue or weakness. Many women initially attribute these symptoms to overexertion, stress, or ageing rather than nutritional inadequacy.

As deficiency progresses, neurological symptoms may emerge, including numbness or tingling in the extremities, heightened anxiety, irritability, and difficulty concentrating. Some women report increased premenstrual symptoms or mood disturbances, though the relationship between magnesium status and these conditions requires further research. Sleep disturbances, including difficulty falling asleep or maintaining sleep, may also occur with low magnesium levels.

Cardiovascular manifestations can include palpitations, irregular heartbeat (arrhythmias), or blood pressure changes. Severe deficiency may precipitate more serious cardiac complications, though this typically occurs only in cases of significant, prolonged depletion or in individuals with underlying health conditions.

Certain groups face increased risk of deficiency, including women with gastrointestinal disorders (Crohn's disease, coeliac disease, chronic diarrhoea), type 2 diabetes, those taking certain medications (proton pump inhibitors, diuretics, some antibiotics), and older adults due to reduced absorption and increased urinary losses. Excessive alcohol consumption also impairs magnesium absorption and increases renal excretion.

If you experience persistent symptoms suggestive of magnesium deficiency, consult your GP. Diagnosis typically involves serum magnesium testing, though this may not accurately reflect total body stores as most magnesium resides intracellularly. Seek urgent medical attention if you experience severe palpitations, chest pain, seizures, or profound weakness, as these may indicate serious medical conditions requiring immediate assessment.

Best Food Sources of Magnesium for Women

A varied, whole-food diet provides the most effective and safest means of meeting magnesium requirements. Green leafy vegetables rank among the richest sources, as magnesium forms the central atom in chlorophyll molecules. According to McCance and Widdowson's Composition of Foods Integrated Dataset (the UK standard food composition tables), a 100g serving of cooked spinach delivers approximately 80 mg of magnesium. These vegetables also supply additional nutrients including folate, iron, and vitamin K, making them particularly valuable for women's health.

Nuts and seeds offer concentrated magnesium sources ideal for snacking or meal enhancement. Pumpkin seeds lead the category with approximately 550 mg per 100g, whilst a typical 30g portion provides around 165 mg. Almonds contain about 270 mg per 100g, with a small handful (30g) contributing roughly 80 mg—nearly one-third of the daily requirement. Chia seeds and flaxseeds also provide significant amounts alongside beneficial omega-3 fatty acids and fibre.

Whole grains retain magnesium in their bran and germ, unlike refined grains where processing removes these nutrient-dense components. Brown rice, quinoa, wholemeal bread, and oats all contribute meaningfully to daily intake. A 100g serving of cooked quinoa provides approximately 65 mg of magnesium.

Legumes, including black beans, chickpeas, lentils, and kidney beans, offer 40–80 mg per cooked 100g serving whilst simultaneously providing protein, fibre, and iron—nutrients of particular importance for women, especially those following plant-based diets. Dark chocolate (70% cocoa or higher) provides approximately 230 mg per 100g, though should be consumed in moderation due to calorie and sugar content—a typical 30g portion provides about 70 mg.

Fish, particularly mackerel, salmon, and halibut, contribute both magnesium and omega-3 fatty acids. Avocados, bananas, and dried figs provide moderate amounts alongside other beneficial nutrients. Incorporating a variety of these foods daily helps ensure adequate intake whilst supporting overall nutritional balance.

When to Consider Magnesium Supplements

Whilst dietary sources remain preferable, supplementation may prove appropriate in specific circumstances. Consider discussing magnesium supplements with your GP or a registered dietitian if you have diagnosed deficiency, confirmed through blood tests and clinical assessment, or if you belong to a high-risk group unable to meet requirements through diet alone due to malabsorption conditions, medication interactions, or dietary restrictions.

Women experiencing persistent symptoms potentially related to inadequate magnesium—such as frequent muscle cramps, significant premenstrual symptoms, or chronic fatigue—may benefit from a trial of supplementation under medical guidance. However, these symptoms have multiple potential causes, and supplementation should not replace proper medical evaluation.

Several magnesium formulations exist, with varying absorption rates and tolerability. Magnesium citrate, glycinate, and malate demonstrate good bioavailability and generally cause fewer gastrointestinal side effects than magnesium oxide, which has lower absorption but costs less. Magnesium glycinate may prove particularly suitable for women seeking to avoid laxative effects. In the UK, magnesium supplements are regulated as food supplements under food law (overseen by the Food Standards Agency and local authorities), not as medicines.

The safe upper limit for supplemental magnesium (excluding dietary sources) is 400 mg per day for adults, as established by the UK Expert Group on Vitamins and Minerals. This is a guidance level for adults unless advised otherwise by a healthcare professional. Exceeding this amount may cause diarrhoea, nausea, and abdominal cramping. Very high doses can lead to serious complications including hypotension, cardiac arrhythmias, and respiratory depression, particularly in individuals with renal impairment.

Important contraindications include kidney disease, as impaired renal function reduces magnesium excretion, potentially leading to dangerous accumulation. Women taking certain medications should consult their GP before supplementing, as interactions may occur. For example, separate magnesium supplements by at least 2 hours from tetracycline/quinolone antibiotics and bisphosphonates, and 4 hours from levothyroxine. Always inform healthcare providers about all supplements you take, and never exceed recommended doses without medical supervision. If you experience adverse effects from any medicine, report them through the MHRA Yellow Card scheme (website or app).

Frequently Asked Questions