In the first article of this three-part series, we reviewed the interaction between Vitamin C and iron as well as vitamin D and calcium, and the ability of these vitamins and minerals to work together to perform various important functions in the body. In the second article, we looked at the minerals phosphorus, magnesium, and potassium. In this third and final article, we will look at a few lesser known, but still vitally important vitamins and minerals: Vitamin A, Vitamin K, Chromium, and Zinc.

Vitamin A and vitamin K are fat-soluble vitamins. Fat-soluble vitamins are different than water-soluble vitamins in that they require bile to be absorbed. The body maintains consistent levels of fat-soluble vitamins by pulling these vitamins from storage as needed. Thus, people can generally eat less than their daily need for these vitamins for days, weeks, or even longer without any damaging effects. However, because fat-soluble vitamins are not as easily removed from the body, the risk of toxicity is much greater than is the risk with water-soluble vitamins.

Vitamin A was the first fat-soluble vitamin to be recognized. Vitamin A has many roles in the body including promoting vision, protein building, and supporting reproduction and growth. Most of the body’s vitamin A is stored in the liver. If a person were to stop eating foods containing vitamin A, deficiency symptoms may not appear for over a year in a healthy adult. The effects of vitamin A deficiency include increased death from infectious diseases (most often in developing countries), anemia, diarrhea, blindness and night blindness, and increased roughness or dryness of the skin.

Recommended Intake for Vitamin A

Foods high in vitamin A include fortified milk, cheese, fortified margarine, eggs, liver, dark/leafy greens, and deep orange fruits and vegetables (squash, carrots, pumpkin). Vitamin A toxicity does occur and is often due to supplementation versus eating plant foods high in vitamin A. Symptoms of vitamin A toxicity include slowed blood clotting time or increased bleeding, as well as stunted growth, nausea, vomiting, diarrhea, skin irritation, headaches, and bone and joint pain.

Vitamin K, the other fat-soluble vitamin previously mentioned, is different than many other vitamins and minerals in that it can be obtained from a source that is not food. Bacteria in the gut are able to create vitamin K, which is later absorbed into the body. Vitamin K has functions in the body including blood clotting and the creation of bone proteins.

Most people eat a diet adequate in vitamin K. However, vitamin K deficiency can occur and is most often due to fat malabsorption (because vitamin K is a fat-soluble vitamin) or medication interactions. Examples of medications that can affect vitamin K levels include antibiotics and anticoagulant drugs. Antibiotics, although designed to kill undesirable bacteria, also often kill off the vitamin K-producing bacteria in the intestine. The most common vitamin K deficiency is caused by treatment with anticoagulant medications. Anticoagulant drugs such as warfarin, inhibit the activity of vitamin K.
Toxicity of vitamin K is also uncommon, but can occur when vitamin K supplements are prescribed. Vitamin K toxicity causes symptoms such as jaundice, brain damage, and damage to red blood cells.
Recommended Intake for Vitamin K
Age Group    Age in Years    Vitamin K
(μg/day)
Children    1-3 years
4-8 years    30
55
Males    9-13 years
14-18 years
19+ years    60
75
120
Females    9-13 years
14-18 years
19+ years    60
75
90

Vitamin K sources in the diet include liver, leafy green vegetables, cabbage-like vegetables, and milk. As previously mentioned, another significant source of vitamin K is from bacterial synthesis in the digestive tract.
Chromium is considered a trace mineral, which means that it is required in the human body in amounts less than 5 grams. Chromium has many functions in the body including its involvement in carbohydrate and fat metabolism, and maintaining blood glucose levels. In 1959, chromium was identified as an element that can improve insulin action and improve glucose tolerance in rats. Other studies later confirmed this action in humans as well.
Adequate Intake for Chromium
Age Group    Age in Years    Chromium
(μg/day)
Children    1-3 years
4-8 years    11
15
Males    9-13 years
14-50 years
51+ years    25
35
30
Females    9-13 years
14-18 years
19-50 years
51+ years    21
24
25
20

Chromium is found in a variety of foods but in often-small quantities. The best sources of chromium in our diets include liver, brewer’s yeast, whole grains, nuts and cheeses. People who consume a diet primarily of refined foods may not eat enough chromium. If you are considering taking a chromium supplement, please speak with your physician about whether this is right for you. Your physician may also recommend a certain form of chromium supplementation, as some forms may be considered safer than others.
Zinc is also a trace element. Zinc is found in almost all cells, but its highest concentrations are found in the muscle and bone. Zinc is a cofactor for more than 100 enzymes. Cofactors work with enzymes to cause chemical reactions in the body. Other functions of zinc include immune function, growth and development, synthesis, storage and release of insulin, blood clotting, taste perception, wound healing, and fetal development.
Zinc deficiency was first reported in the 1960s in young Middle Eastern children. Middle Eastern diets are often low in meats (a rich source of zinc) and high in legumes. Although legumes are very healthy, they do contain phytates and fiber, which have been known to inhibit the absorption of zinc. Zinc deficiency may occur due to poor intake, malabsorption, increased zinc losses, and poor usage of zinc by the body. Symptoms of zinc deficiency include growth retardation, slowed sexual maturation, diarrhea, impaired immune response, poor motor development, taste changes, and slowed wound healing. Certain groups are more at risk for zinc deficiency such as pregnant women, young children, the elderly and the very poor.
Recommended Intake for Zinc
Age Group    Age in Years    Zinc
(mg/day)
Children    1-3 years
4-8 years    3
5
Males    9-13 years
14+ years    8
11
Females    9-13 years
14-18 years
19+ years    8
9
8

Zinc toxicity generally only occurs with supplementation and can lead to symptoms such as vomiting, diarrhea, dizziness, headaches, and fatigue. Sources of zinc include meats, shellfish, poultry, liver, whole grains, and yogurt. Many Americans also get zinc from fortified breakfast cereals or other fortified products.
For many people, eating a balanced diet is sufficient to get all the nutrients needed each day. The labeling and marketing of many vitamin and mineral supplements can often seem very appealing, and many people are drawn to the thought of how easy it may be to take a supplement instead of eating balanced diet. If you are considering taking a vitamin or mineral supplement, speak with your healthcare provider or registered dietitian to determine if supplementation is right for you.