ミネラル (栄養素)

栄養の文脈では、ミネラルとは化学元素のことである。一部の「ミネラル」は生命にとって必須であるが、ほとんどはそうではない。ミネラルは必須栄養素の4つのグループの1つであり、他にはビタミン、必須脂肪酸、必須アミノ酸がある。人体の5大ミネラルは、カルシウム、リン、カリウム、ナトリウム、マグネシウムである。残りの元素は「trace element」と呼ばれる。一般的に受け入れられている微量元素は、鉄、塩素、コバルト、銅、亜鉛、マンガン、モリブデン、ヨウ素、セレンである；もっとあるかもしれないという証拠もある。

炭酸脱水酵素は、亜鉛を必要とする酵素（この画像の中央付近にある灰色の球体）で、二酸化炭素の呼気に不可欠である。

炭素、水素、酸素、窒素）（CHON）の4元素が人体の96重量％を占める。 これらの元素は通常、栄養ミネラルのリストには含まれていない。 これらの元素はマクロミネラルと呼ばれることもある。マイナーミネラル（微量元素とも呼ばれる）は残りを構成し、通常、食事中のミネラルに関する議論の焦点となる。

植物は土壌からミネラルを得る。植物は動物に摂取されることで、ミネラルを食物連鎖の上に移動させる。大型の生物は土壌を消費したり（地食い）、塩舐めなどの鉱物資源を利用してミネラルを得ることもある。

最後に、ミネラルと元素は多くの点で同義語であるが、ミネラルは生物学的利用吸収可能な程度にしか存在しない。吸収されるためには、ミネラルは可溶性であるか、摂取した生物が容易に抽出できるものでなければならない。 例えば、モリブデンは必須ミネラルだが、金属モリブデンには栄養学的な利点はない。 多くのモリブデン酸塩はモリブデンの供給源である。

ヒトの必須化学元素

詳細は「Composition of the human body/ja」を参照

構造的・機能的な役割を果たすことで、ヒトの生化学的プロセスをサポートするために必要な化学元素は19種類知られており、さらに10種類程度の証拠がある。

酸素、水素、炭素、窒素は体内で最も重量の多い元素で、人体の重量の約96％を占める。カルシウムは成人体重の920～1200グラムを占め、その99％は骨と歯に含まれている。これは体重の約1.5％にあたる。リンはカルシウムの約2/3の量で、体重の約1％を占める。他の主要ミネラル（カリウム、ナトリウム、塩素、硫黄、マグネシウム）は、体重の約0.85％を占めるに過ぎない。これら11の化学元素（H、C、N、O、Ca、P、K、Na、Cl、S、Mg）を合わせて、身体の99.85％を占める。残りの～18種類の超微量ミネラルは、身体のわずか0.15％、平均的な人で合計約100グラムを構成している。この段落の分数の合計は、人体の化学組成の記事からパーセンテージを合計した量である。

ヒト（および他の哺乳類）における様々な超微量元素の必須性については、同じデータに基づいても、いくつかの多様な意見が存在する。例えば、クロムがヒトにおいて必須であるかどうかは議論されている。クロムを含む生化学物質は精製されていない。米国と日本はクロムを必須栄養素に指定しているが、欧州連合を代表する欧州食品安全機関（EFSA）は2014年にこの問題を検討し、同意していない。

既知のミネラル栄養素や示唆されているミネラル栄養素のほとんどは、比較的原子量が低く、陸上や、ナトリウムとヨウ素については海洋でそれなりに一般的である。そのような可溶性化合物を持たない元素は、非必須元素（Al）か、せいぜい微量（Si）しか必要とされない傾向がある。

Essential elements for higher organisms (eucarya).
H																	He
Li	Be											B	C	N	O	F	Ne
Na	Mg											Al	Si	P	S	Cl	Ar
K	Ca	Sc	Ti	V	Cr	Mn	Fe	Co	Ni	Cu	Zn	Ga	Ge	As	Se	Br	Kr
Rb	Sr	Y	Zr	Nb	Mo	Tc	Ru	Rh	Pd	Ag	Cd	In	Sn	Sb	Te	I	Xe

Legend:   The four basic organic elements   Quantity elements   Essential trace elements   Essentiality or function debated

生物学的プロセスにおける役割

Dietary element	RDA/AI Male/Female (US) [mg]	UL (US and EU) [mg]	Category	High nutrient density dietary sources	Terms for deficiency/excess
Potassium	4700	NE; NE	A systemic electrolyte and is essential in coregulating ATP with sodium	Sweet potato, tomato, potato, beans, lentils, dairy products, seafood, banana, prune, carrot, orange	hypokalemia / hyperkalemia
Chlorine	2300	3600; NE	Needed for production of hydrochloric acid in the stomach, in cellular pump functions and required in host defense	Table salt (sodium chloride) is the main dietary source.	hypochloremia / hyperchloremia
Sodium	1500	2300; NE	A systemic electrolyte and is essential in coregulating ATP with potassium	Table salt (sodium chloride, the main source), sea vegetables, milk, and spinach.	hyponatremia / hypernatremia
Calcium	1000	2500; 2500	Needed for muscle, heart and digestive system health, builds bone (see hydroxyapatite), supports synthesis and function of blood cells, helps in blood clotting	Dairy products, eggs, canned fish with bones (salmon, sardines), green leafy vegetables, nuts, seeds, tofu, thyme, oregano, dill, cinnamon.	hypocalcaemia / hypercalcaemia
Phosphorus	700	4000; 4000	A component of bones (see hydroxyapatite), cells, in energy processing, in DNA and ATP (as phosphate) and many other functions	Red meat, dairy foods, fish, poultry, bread, rice, oats. In biological contexts, usually seen as phosphate	hypophosphatemia / hyperphosphatemia
Magnesium	420/320	350; 250	Required for processing ATP and for bones	Spinach, legumes, nuts, seeds, whole grains, peanut butter, avocado	hypomagnesemia (magnesium deficiency) / hypermagnesemia
Iron	8/18	45; NE	Required for many proteins and enzymes, notably hemoglobin to prevent anemia	Meat, seafood, nuts, beans, dark chocolate	iron deficiency / iron overload disorder
Zinc	11/8	40; 25	Required for several classes of enzymes such as matrix metalloproteinases, liver alcohol dehydrogenase, carbonic anhydrase and zinc finger proteins	Oysters*, red meat, poultry, nuts, whole grains, dairy products	zinc deficiency / zinc toxicity
Manganese	2.3/1.8	11; NE	Required co-factor for superoxide dismutase	Grains, legumes, seeds, nuts, leafy vegetables, tea, coffee	manganese deficiency / manganism
Copper	0.9	10; 5	Required co-factor for cytochrome c oxidase	Liver, seafood, oysters, nuts, seeds; some: whole grains, legumes	copper deficiency / copper toxicity
Iodine	0.150	1.1; 0.6	Required for the synthesis of thyroid hormones and to help enzymes in host defense	Seaweed (kelp or kombu)*, grains, eggs, iodized salt	iodine deficiency (goiter) / iodism (hyperthyroidism)
Molybdenum	0.045	2; 0.6	Required for the functioning of xanthine oxidase, aldehyde oxidase, and sulfite oxidase	Legumes, whole grains, nuts	molybdenum deficiency / molybdenum toxicity
Selenium	0.055	0.4; 0.3	Essential to activity of antioxidant enzymes like glutathione peroxidase	Brazil nuts, seafoods, organ meats, meats, grains, dairy products, eggs	selenium deficiency / selenosis
Cobalt	none	NE; NE	Cobalt is available for use by animals only after having been processed into complex molecules (e.g., vitamin B12) by bacteria. Humans contain only milligrams of cobalt in these cofactors. A deficiency of cobalt leads to pernicious anemia.	Animal muscle and liver are good dietary sources, also shellfish and crab meat.	pernicious anemia / cobalt poisoning

RDA = Recommended Dietary Allowance; AI= Adequate intake; UL = Tolerable upper intake level; Figures shown are for adults age 31–50, male or female neither pregnant nor lactating

* One serving of seaweed exceeds the US UL of 1100 μg but not the 3000 μg UL set by Japan.

Dietary nutrition

Dietitians may recommend that minerals are best supplied by ingesting specific foods rich with the chemical element(s) of interest. The elements may be naturally present in the food (e.g., calcium in dairy milk) or added to the food (e.g., orange juice fortified with calcium; iodized salt fortified with iodine). Dietary supplements can be formulated to contain several different chemical elements (as compounds), a combination of vitamins and/or other chemical compounds, or a single element (as a compound or mixture of compounds), such as calcium (calcium carbonate, calcium citrate) or magnesium (magnesium oxide), or iron (ferrous sulfate, iron bis-glycinate).

The dietary focus on chemical elements derives from an interest in supporting the biochemical reactions of metabolism with the required elemental components. Appropriate intake levels of certain chemical elements have been demonstrated to be required to maintain optimal health. Diet can meet all the body's chemical element requirements, although supplements can be used when some recommendations are not adequately met by the diet. An example would be a diet low in dairy products, and hence not meeting the recommendation for calcium.

Plants

Structure of the Mn₄O₅Ca core of the oxygen-evolving site in plants, illustrating one of many roles of the trace mineral manganese.

The list of minerals required for plants is similar to that for animals. Both use very similar enzymes, although differences exist. For example, legumes host molybdenum-containing nitrogenase, but animals do not. Many animals rely on hemoglobin (Fe) for oxygen transport, but plants do not. Fertilizers are often tailored to address mineral deficiencies in particular soils. Examples include molybdenum deficiency, manganese deficiency, zinc deficiency, and so on.

Safety

The gap between recommended daily intake and what are considered safe upper limits (ULs) can be small. For example, for calcium the U.S. Food and Drug Administration set the recommended intake for adults over 70 years at 1,200 mg/day and the UL at 2,000 mg/day. The European Union also sets recommended amounts and upper limits, which are not always in accord with the U.S. Likewise, Japan, which sets the UL for iodine at 3000 μg versus 1100 for the U.S. and 600 for the EU. In the table above, magnesium appears to be an anomaly as the recommended intake for adult men is 420 mg/day (women 350 mg/day) while the UL is lower than the recommended, at 350 mg. The reason is that the UL is specific to consuming more than 350 mg of magnesium all at once, in the form of a dietary supplement, as this may cause diarrhea. Magnesium-rich foods do not cause this problem.

Elements considered possibly essential for humans but not confirmed

Many ultratrace elements have been suggested as essential, but such claims have usually not been confirmed. Definitive evidence for efficacy comes from the characterization of a biomolecule containing the element with an identifiable and testable function. One problem with identifying efficacy is that some elements are innocuous at low concentrations and are pervasive (examples: silicon and nickel in solid and dust), so proof of efficacy is lacking because deficiencies are difficult to reproduce. Ultratrace elements of some minerals such as silicon and boron are known to have a role but the exact biochemical nature is unknown, and others such as arsenic are suspected to have a role in health, but with weaker evidence. In particular, trace arsenic seems to have a positive effect on some organisms, but so does lead, showcasing the uncertainty behind whether some trace elements are truly essential. Strontium is tolerated and is a component of some drugs, but it is not essential, only beneficial. Non-essential elements can sometimes appear in the body when they are chemically similar to essential elements (e.g. Rb⁺ and Cs⁺ replacing Na⁺), so that essentiality is not the same thing as uptake by a biological system.

Element	Description	Excess
Bromine	Possibly important to basement membrane architecture and tissue development, as a needed catalyst to make collagen IV.	bromism
Arsenic	Essential in rat, hamster, goat and chicken models, but no research has been done in humans.	arsenic poisoning
Nickel	Nickel is an essential component of several enzymes, including urease and hydrogenase. Although not required by humans, some are thought to be required by gut bacteria, such as urease required by some varieties of Bifidobacterium. In humans, nickel may be a cofactor or structural component of certain metalloenzymes involved in hydrolysis, redox reactions and gene expression. Nickel deficiency depressed growth in goats, pigs, and sheep, and diminished circulating thyroid hormone concentration in rats.	Nickel toxicity
Fluorine	Might have a role in biologic mineralisation, and fluoride deficiency symptoms have been found in goats, but there is no clear evidence of essentiality in humans. Research indicates that the primary dental benefit from fluoride occurs at the surface from topical exposure. However, even if not essential, fluorine would still be a beneficial element for this reason. Of the minerals in this table, fluoride is the only one for which the U.S. Institute of Medicine has established an Adequate Intake.	Fluoride poisoning
Boron	Boron is an essential plant nutrient, required primarily for maintaining the integrity of cell walls. Boron has been shown to be essential to complete the life cycle in representatives of all kingdoms of life. In animals, supplemental boron has been shown to reduce calcium excretion and activate vitamin D.	No acute effects (LD50 of boric acid is 2.5 grams per kilogram body weight)
Lithium	Based on plasma lithium concentrations, biological activity and epidemiological observations, there is evidence, not conclusive, that lithium is an essential nutrient.	Lithium toxicity
Chromium	Proposed to be involved in glucose and lipid metabolism, although its mechanisms of action in the body and the amounts needed for optimal health are not well-defined	chromium deficiency / chromium toxicity
Silicon	Deficiency symptoms have been found in chickens and rats, though not humans. Circumstantial evidence suggests that it is an essential nutrient, probably having an effect on the function and composition of brain and bone.
Vanadium	Has an established, albeit specialized, biochemical role in other organisms (algae, lichens, fungi, bacteria), and there is significant circumstantial evidence for its essentiality in humans. It is rather toxic for a trace element and the requirement, if essential, is probably small.
Tin	Rats fed a tin-free diet exhibited improper growth, but the evidence for essentiality is otherwise limited.	Tin poisoning
Other	Tungsten, the early lanthanides, and cadmium have specialized biochemical uses in certain lower organisms, but these elements appear not to be used by mammals.

Mineral ecology

Main article: Biomineralization

Diverse ions are used by animals and microorganisms for the process of mineralizing structures, called biomineralization, used to construct bones, seashells, eggshells, exoskeletons and mollusc shells.

Minerals can be bioengineered by bacteria which act on metals to catalyze mineral dissolution and precipitation. Mineral nutrients are recycled by bacteria distributed throughout soils, oceans, freshwater, groundwater, and glacier meltwater systems worldwide. Bacteria absorb dissolved organic matter containing minerals as they scavenge phytoplankton blooms. Mineral nutrients cycle through this marine food chain, from bacteria and phytoplankton to flagellates and zooplankton, which are then eaten by other marine life. In terrestrial ecosystems, fungi have similar roles as bacteria, mobilizing minerals from matter inaccessible by other organisms, then transporting the acquired nutrients to local ecosystems.

See also

• Food composition
• Human nutrition
• Micronutrient
• Mineral deficiency

さらに読む

• Humphrey Bowen (1979) Environmental Chemistry of the Elements. Academic Press, ISBN 0-12-120450-2.
• Humphry Bowen (1966) Trace Elements in Biochemistry. Academic Press.

外部リンク

• "Vitamins and minerals". nhs.uk. 23 October 2017.
• Concept of a nutritious food: toward a nutrient density score
• Metals in Nutrition