2.3 Micronutrients: vitamins and minerals

Vitamins

Vitamins are organic compounds your body needs in small amounts to carry out critical functions, from energy metabolism to immune defense. They're split into two categories based on how they dissolve and move through your body.

Types of Vitamins

Fat-soluble vitamins dissolve in fat and get stored in your body's fatty tissue and liver. These include vitamins A, D, E, and K. Because your body holds onto them, excessive intake over time can build up and lead to toxicity. This is why megadosing fat-soluble vitamin supplements can actually be dangerous.

Water-soluble vitamins dissolve in water and aren't stored in significant amounts. This group includes vitamin C and the B-complex vitamins (thiamine, riboflavin, niacin, pantothenic acid, biotin, B6, B12, and folate). Your kidneys filter out excess amounts through urine, so toxicity is much less likely. The tradeoff is that you need a consistent daily supply from your diet.

Vitamin Deficiency and Antioxidants

Vitamin deficiency occurs when your body doesn't get enough of a specific vitamin over time. The causes include inadequate dietary intake, malabsorption disorders (like celiac disease), or increased requirements (during pregnancy, for example). Classic deficiency diseases include:

• Scurvy from vitamin C deficiency, which impairs collagen synthesis and causes bleeding gums and poor wound healing
• Rickets from vitamin D deficiency, which leads to soft, weak bones in children

Antioxidants are substances that protect your cells from damage caused by free radicals, which are unstable molecules produced during normal metabolism and by environmental stressors like UV radiation. Vitamins C and E act as antioxidants, along with other compounds like carotenoids and polyphenols found in fruits, vegetables, and tea. By neutralizing free radicals, antioxidants help reduce the risk of chronic diseases such as cardiovascular disease and certain cancers.

Minerals

Minerals are inorganic elements your body can't produce on its own. Like vitamins, they're essential in small quantities, but they're categorized by how much your body requires daily.

Macrominerals and Trace Minerals

Macrominerals are needed in amounts greater than 100 mg per day. These include calcium, phosphorus, magnesium, sodium, potassium, chloride, and sulfur. They handle large-scale jobs in the body:

• Calcium and phosphorus are the primary structural components of bones and teeth
• Sodium and potassium regulate fluid balance and nerve impulse transmission
• Magnesium supports hundreds of enzymatic reactions, including energy production

Trace minerals are needed in amounts less than 100 mg per day. These include iron, zinc, copper, manganese, iodine, fluoride, selenium, and chromium. Despite the tiny quantities required, they're just as essential. Iron, for instance, is a core component of hemoglobin, which carries oxygen in your blood. Iodine is necessary for thyroid hormone production, and zinc supports immune function and wound healing.

Mineral Bioavailability

Not all of the mineral content in your food actually gets absorbed. Bioavailability refers to the proportion of a mineral that your body absorbs and can use. Several factors influence this:

• Chemical form of the mineral: Heme iron (from animal sources like red meat) is absorbed at roughly 15–35%, while non-heme iron (from plant sources like spinach) is absorbed at only about 2–20%.
• Enhancers: Certain compounds boost absorption. Vitamin C significantly increases non-heme iron absorption, which is why pairing citrus fruits with iron-rich plant foods is a common recommendation.
• Inhibitors: Phytates (found in whole grains and legumes) and oxalates (found in spinach and rhubarb) bind to minerals and reduce absorption.
• Individual nutritional status: If your body is deficient in a mineral, it often upregulates absorption to compensate.

Practical strategies to improve bioavailability:

1. Eat vitamin C-rich foods (bell peppers, citrus) alongside iron-rich meals
2. Soak or sprout grains and legumes before cooking to reduce phytate content
3. Choose more bioavailable mineral forms when possible (heme iron over non-heme iron)

Micronutrient Recommendations and Fortification

Recommended Daily Allowance (RDA)

The Recommended Daily Allowance (RDA) is the average daily intake level sufficient to meet the nutrient requirements of nearly all (97–98%) healthy individuals in a given age and gender group. RDAs are established by the Food and Nutrition Board of the National Academies of Sciences, Engineering, and Medicine, and they're based on scientific evidence from human studies.

RDAs vary by age, sex, and life stage. A pregnant woman, for example, needs 600 µg of folate per day compared to 400 µg for most adults. These values serve as goals for individual intake and as reference points for food labeling and fortification programs. They're updated periodically as new research emerges.

Fortification

Fortification is the process of adding micronutrients to food products to boost their nutritional value. This is a major public health tool for preventing deficiencies across entire populations.

Fortification comes in two forms:

• Mandatory fortification is required by law and targets widespread public health concerns. A well-known example is the addition of folic acid to enriched grain products in the U.S. (since 1998), which significantly reduced the incidence of neural tube defects in newborns. Iodized salt is another example, introduced to prevent goiter and other iodine deficiency disorders.
• Voluntary fortification is initiated by food manufacturers to enhance their products' nutritional profiles. Calcium-fortified orange juice and vitamin D-fortified plant milks are common examples.

Commonly fortified foods include cereals, milk, salt, and flour. When you see "enriched" on a label, that typically means nutrients lost during processing have been added back. "Fortified" means nutrients not originally present (or present in lower amounts) have been added.