Magnesium

Magnesium is thought to be involved in more than 300 metabolic reactions in the human body, some of which include;

• synthesis of deoxyribonucleic acid (DNA), ribonucleic acid (RNA), amino acids and lipids
• metabolism of carbohydrates and fats to produce cellular energy in the form of ATP
• structural roles in bone, teeth and cell membrane formation 
• active transport of ions such as calcium and potassium across cell membranes

To relate this to portion size, highlighted below are some foods that will help you to achieve your magnesium reference intake;

• 200 g serving of tofu yields 46 mg of magnesium
• 28 g cashew nuts yields 81 mg of magnesium
• 200 g fillet of halibut yields 52 mg of magnesium
• 28 g serving of wheat germ yields 67 mg of magnesium
• 200 ml serving of whole milk yields 25 mg of magnesium
• 200 g serving of chicken breast yields 58 mg of magnesium

Due to it's widespread distribution in plant and animal foods, magnesium deficiency is rare in those who adhere to a balanced diet. Furthermore, to maintain magnesium status, urinary excretion of magnesium is reduced when intake is low. However, the presence of gastrointestinal or renal disorders, alcoholism, or sub-optimal intake in elderly populations are strong risk factors for magnesium deficiency. Severe deficiency may result in low blood calcium and potassium, the retention of sodium, and the development of symptoms such as tremors, muscle spasms, personality changes, decreased appetite, nausea and vomiting. 

While excess magnesium can inhibit bone calcification, high dietary intake, including supplements, is unlikely to result in toxicity.

Imbalances to the calcium/phosphorous ratio, low vitamin D levels, excessive alcohol intake, and diuretics are some factors thought to hinder the uptake of magnesium.

Vitamins B_1, B_6, C and D, and minerals such as calcium, zinc and phosphorous may assist the uptake of magnesium.