nutrition

Nutrition 101 and Optometry: PART 2

By learning about the micronutrients, you may help to prevent nutritional deficiencies that can lead to disease.

JEFFREY ANSHEL, O.D., Carlsbad, C A.
AND ELLEN TROYER, M.T., M.A., Colorado Springs, CO.

It's essential you obtain a basic knowledge of the micronutrients because peer-reviewed science strongly suggests that nutrient deficiencies affect both the body and the eye through a number of mechanisms, including gene transcription.

By educating your patients that nutrient intake is a good predictor of both present and future disease, you may prompt them to pay better attention to their diets, which in turn, may not only help curb the U.S. overweight/obesity and malnourishment epidemics, but the onset of eye disease, such as dry eye, as well.

In addition, consider this: A 2008 Healthcare Professionals Impact Study found that 72% of physicians and 89% of nurses use dietary supplements. Additionally, 79% of all physicians and 82% of all nurses now recommend dietary supplements to their patients. Why should optometrists and optometry patients be any different?

A caveat: Because the nutrient chemicals of life act in balanced concert with one another, it's essential your patients meet the baseline of these nutrients on a daily basis prior to your offering or recommending supplementation.

As was the case with part one of this two part series, no specific guidelines currently exist for optometrists on how, specifically, to initiate conversations with patients about their nutrient intake. The Optometric Nutrition Society (www.optometricnutritionsociety.org) is currently designing a patient intake nutrition form for optometrists so that you can enhance your role as a member of your patient's healthcare team.

The fat soluble vitamins

Four vitamins comprise this category:

► Vitamin A. This vitamin plays an important role in vision, bone growth, reproduction, cell division and cell differentiation. It helps regulate the immune system, which helps prevent or fight infections. Also, Vitamin A may help lymphocytes fight infections more effectively. The hydrocarbon carotenoid, beta carotene, converts to vitamin A retinol, only if the liver stores are depleted, but this conversion becomes less dependable as we age.¹ Therefore, you shouldn't consider beta carotene a good source of supplemental Vitamin A.

Since retinol is produced in the retina from vitamin A, it's obviously a critical nutrient for healthy vision.

For information on foods containing vitamin A and their recommended dietary allowances (RDA) for both children and adults, visit http://ods.od.nih.gov/factsheets/vitamina.asp.

► Vitamin D. Known as the "sunshine" vitamin, vitamin D plays an important role in the maintenance of organ systems and bone. It affects the immune system by promoting immune functions, such as phagocytosis and anti-tumor activity.

While this vitamin doesn't have any direct effects on the eye, it's important to maintain a balance of vitamin D with vitamin A to reduce the risk of hip fracture in the elderly.²

For information on foods containing vitamin D and their RDA for children and adults, visit http://ods.od.nih.gov/factsheets/vitamind.asp.

We expect the RDA will increase to between 1,200 to 2,000 International Units (IU) within the next few years, given the vast amount of new vitamin D research linking vitamin D deficiency to most degenerative disease, such as rheumatoid arthritis.²

► Vitamin E. This vitamin is composed of a group of compounds called tocopherols. Alpha tocopherol is the most active biological antioxidant in humans.³ The natural and safest form is d-tocopherol, and the synthetic, and far less expensive and less effective form, is dl-tocopherol.³ Vitamin E is an excellent antioxidant and also causes dilation of the blood vessels — permitting a fuller flow of blood to many organs. As a powerful antioxidant, it helps reduce the effects of reactive oxygen species in degeneration of the rod outer segments in the retina.⁴

For information on foods containing vitamin E and their RDA for children and adults, visit http://ods.od.nih.gov/factsheets/vitamine.asp#h3.

► Vitamin K. Vitamin K is known as the clotting vitamin, and it can be an important player in bone health.⁵ If your patients take anticoagulants, you should know that vitamin K, or foods containing vitamin K, can affect how these drugs work. Specifically, sudden increases in vitamin K intake can decrease the anticoagulant's ability to prolong the usual time it takes for a clot to form.⁶ Blood coagulation is significant in many retinal diseases, such as diabetic retinopathy.⁷ Most multiple vitamins no longer include vitamin K because such a large percentage of the population uses natural or pharmaceutical blood thinning therapy.⁸

For information on foods containing vitamin K, visit http://ods.od.nih.gov/factsheets/cc/coumadin1.pdf. For information on adequate intake, visit http://lpi.oregonstate.edu/infocenter/vitamins/vitaminK/.

Water soluble vitamins

The B-complex vitamins are B1 (thiamine), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B12 (cobalamin) and folic acid. The grouping of these water-soluble compounds under the term "B complex" is based on their common sources, their close relationship in vegetable and animal tissues and their functional relationships.

The B-complex vitamins are active in providing the body with energy basically by converting carbohydrates into glucose, which the body burns to produce energy. These vitamins are vital to deoxyribonucleic acid (DNA) protection and repair and for the metabolism of fats and protein. Also, the B vitamins are necessary for the normal functioning of the nervous system. Brewer's yeast is an excellent source of the B-complex group. One should take all the B vitamins together because they are similar in structure and work in synergy with each other. The only B vitamin that the Institute of Medicine (IOM) has established an upper limit (UL) for is vitamin B6, and that limit is 100mg per day.⁹ (The IOM of the National Academies provides the United States with science-based advice on matters of bio-medical science, medicine and health.)

The most important B vitamins are:

► B1. Thiamine combines with pyruvic acid to form a coenzyme necessary for the breakdown of carbohydrates into glucose, which the body then oxidizes to produce energy. Thiamine enhances blood circulation and assists in the formation of blood. It also optimizes cognitive activity and brain function.

Thiamine deficiency can lead to optic neuritis, as well as to impairment of the central nervous system.^10,11

For information on foods containing thiamine and the RDA for adults and children, visit www.nlm.nih.gov/medlineplus/druginfo/natural/patient-thiamin.html.

► B2. Riboflavin is stable to heat, oxidation and acid, but disintegrates in the presence of alkalis or light, especially ultraviolet (UV) light. It functions as part of a group of enzymes involved in the breakdown and utilization of carbohydrates, fats and protein. This vitamin is necessary for cell respiration because it works with enzymes in the utilization of cell oxygen. Riboflavin supports mitochondrial energy production by stimulating metabolism. It also aids in the prevention of many types of eye disorders, such as cataracts.¹²

For information on foods containing riboflavin and the RDA for children and adults, visit www.nlm.nih.gov/medlineplus/druginfo/natural/patient-riboflavin.html.

► B3. Niacin assists in the functioning of the digestive system, skin and nerves. As a coenzyme, niacin works in conjunction with enzymes in the breakdown and utilization of protein, fats and carbohydrates. Also, this vitamin is effective at improving blood circulation and reducing the blood-cholesterol level.

There is no direct effect of niacin in the eye, but its effect on general circulation does include blood circulation in the eye.¹³ In addition, extremely high doses of niacin (more than 2,000mg/day) can cause niacin maculopathy.¹⁴

For information on foods containing niacin and the RDA for children and adults, visit www.nlm.nih.gov/medlineplus/druginfo/natural/patient-niacin.html.

► B5. The body requires pantothenic acid for the conversion of carbohydrates, fats and protein into usable energy. It's necessary for the synthesis of red blood cells, steroid metabolism, and it's vital in the synthesis of fatty acids and cholesterol, among other biological compounds. Pantothenic acid is the precursor of coenzyme A (CoA), which is necessary for mitochondrial adenosine triphosphate (ATP) energy production.

For information on foods containing pantothenic acid and the RDA for children and adults, visit www.nlm.nih.gov/medlineplus/druginfo/natural/patient-vitaminb5.html.

► B6. Pyridoxine consists of three related compounds—pyridoxine, pyridoxal and pyridoxamine. (All three forms are B6, but healthcare professionals commonly refer to B6 as pyridoxine.) The body requires this vitamin for the proper absorption of vitamin B12, and for the production of hydrochloric acid and magnesium. Pyridoxine acts as a co-enzyme in the breakdown and utilization of carbohydrates, fats and protein. The body also needs it to produce antibodies and red blood cells. In addition, it facilitates the release of glycogen for energy from the liver and muscles. The body converts vitamin B6 to pryirdoxal-5 phosphate, which is directly involved in mitochondrial biosynthesis. This form of pyridoxine plays a role in the biosynthesis of four important neurotransmitters: serotonin, epinephrine, norepinephrine and gamma-aminobutyric acid.¹⁵

For information on foods containing Pyridoxine and the RDA for children and adults, visit www.nlm.nih.gov/medlineplus/druginfo/natural/patient-b6.html.

► B12. One cannot synthetically engineer cobalamin. Instead, you must grow it, like penicillin, in bacteria or molds. The two most common forms of supplemental B12 are cyanocobalamin and the more expensive and more absorbable form, methylcobalamin.¹⁶ Because B12 helps maintain healthy nerve cells, it supports optic nerve function.¹⁷ High blood levels of folic acid, common in vegetarians and those who supplement with stand-alone folate, can mask a vitamin B12 deficiency. Therefore, vegetarians frequently have low levels of vitamin B12.¹⁸ Elderly individuals have low levels of this vitamin as well due to age-related loss of the intrinsic factor necessary for B12 absorption. This intrinsic factor is a glycoprotein that the parietal cells of the stomach produce. It's necessary for the absorption of vitamin B12 in the intestine.

For information on foods containing cobalamin and the RDA for children and adults, visit www.nlm.nih.gov/medlineplus/ency/article/002403.htm.

► Folate. Folic acid is the synthetic form of folate found in supplements and added to fortified foods. Folate helps produce and maintain new cells. This is especially important during periods of rapid cell division and growth, such as during infancy and pregnancy. The body needs folate for the optimal function of DNA and ribonucleic acid (RNA). Folate is essential for the metabolism of homocysteine, which helps maintain normal levels of this methionine byproduct. Researchers have found high levels of homocysteine in patients who progress from dry to wet AMD.¹⁹

For information on foods containing folate and RDA for children and adults, visit http://ods.od.nih.gov/factsheets/folate.asp.

The Major minerals

► Calcium. This mineral is the major element in bones and teeth. The body must maintain calcium levels in the blood and fluid surrounding the cells (extra-cellular fluid) within a narrow concentration for normal physiological functioning. The body will actually demineralize bone to maintain normal blood calcium levels if calcium intake is inadequate. The body requires vitamin D, boron and magnesium for optimal calcium absorption.

For information on foods containing calcium and the RDA for children and adults, visit http://ods.od.nih.gov/factsheets/calcium.asp. The calcium safe UL is 2,500mg per day for adults and 800mg for children.⁹

► Magnesium. This mineral is involved in more than 300 essential metabolic reactions, including the metabolism of carbohydrates and fats. The ATP synthesizing protein in mitochondria — the molecule that provides energy for all metabolic processes — requires it. High doses of supplemental zinc interfere with magnesium absorption.²⁰

For information on foods containing magnesium and the RDA for children and adults, visit http://ods.od.nih.gov/factsheets/magnesium.asp. The magnesium safe UL refers only to supplemental magnesium. That number is 350mg per day for adults and about 250mg for children.⁹

► Zinc. This mineral is an essential trace element for all forms of life. It plays important roles in ATP cellular energy, growth and development, the immune response, neurological and retina function and reproduction. Researchers have found that zinc can regulate gene expression by acting as transcription factors that bind to DNA.²¹ This mineral plays a role in cell signaling, and it influences hormone release and nerve-impulse transmission. Researchers have also suggested that zinc plays a role in apoptosis (gene directed cell death).²² The retina contains high concentrations of zinc. Large amounts of supplemental zinc interfere with copper bioavailability, and excess zinc supplementation is now associated with impaired kidney function.²³

For information on foods containing zinc and the RDA for children and adults, visit http://ods.od.nih.gov/factsheets/cc/zinc.html#rda.

► Selenium. We require this mineral for the function of a number of selenium-dependent enzymes, such as glutathione peroxidase and thioredoxin reductase (which indirectly reduce certain oxidized molecules), and three known deiodinase enzymes (which convert one thyroid hormone to another). Selenium is associated with vascular endothelial cells because it acts as an antioxidant that protects them from damage. In addition, it supports the activity of vitamin E in limiting the oxidation of lipids. Therefore, you should take the two nutrients together.

For information on foods containing selenium and the RDA for children and adults, visit http://ods.od.nih.gov/factsheets/selenium.asp.

► Copper. This mineral plays a major role in mitochondria ATP energy production. The body requires it for the cross-linking of collagen and elastin, which are essential for strong and flexible connective tissue. In addition, it's necessary for optimal iron metabolism and essential for normal brain and nervous system function. It works as the superoxide dismutase (SOD) antioxidant, along with zinc, by catalyzing the conversion of superoxide radicals to hydrogen peroxide, which the body then reduces to water.

Excess copper is associated with angiogenesis — particularly important information for the age-related macular degeneration patient.²⁴

For information on foods containing copper and RDA for children and adults, visit www.nlm.nih.gov/medlineplus/ency/article/002419.htm.

► Manganese. This mineral is nutritionally essential because it's part of the powerful manganese superoxide dismutase (MnSOD) — the principal antioxidant enzyme in the mitochondria. Mitochondria consume more than 90% of the oxygen cells use, so they are especially vulnerable to oxidative stress. Again, this is particularly important to retina health because of the high oxidative demand of the retina.

The RDA for manganese is 1.8mg per day, with the safe UL of 11mg per day.²⁵

► Chromium. This mineral participates in glucose metabolism by enhancing the effects of insulin, which binds to insulin receptors on the surface of cells, allowing for cellular glucose uptake.

For examples of foods containing chromium and RDA for children and adults, visit www.nlm.nih.gov/medlineplus/ency/article/002418.htm.

Phytochemicals

The IOM hasn't established RDAs for Phytochemicals.

The phytochemicals:

► Bioflavonoids. These are water-soluble and composed of a group of brightly colored substances that often appear in fruits and vegetables as companions to vitamin C. The major members of the group: hesperidins, rutin and quercetin. The body requires bioflavonoids for the proper absorption and use of vitamin C. In addition, they're important for vascular strength, particularly capillary strength.⁹

► Anthocyanidins. Anthocyanins are water-soluble vascular pigments that may appear red, purple or blue, according to pH. The pigment belongs to a class of molecules called flavonoids. Plants rich in anthocyanins are blueberry, cranberry and bilberry, black raspberry, blackberry, blackcurrant, chokeberry, cherry, eggplant and purple grapes.^26,27

► Proanthocyanidins. Proanthocyanidins are a class of flavones that have a high-antioxidant effect on the body. Some of the more popular proanthyocyanidins are grape seed and resveratrol.²⁸

Plants produce these compounds to increase their resistance to bacteria and fungi. This accounts for the number of beneficial health effects, such as anti-cancer, antiviral, neuroprotective, anti-aging and anti-inflammatory effects that researchers have reported.²⁹

► Carotenoids. Carotenoids are naturally occurring organic pigments that make our food different colors but also contain powerful antioxidant properties. Almost 600 known carotenoids exist.³⁰

The two classes of carotenoids are xanthophyll (lutein and zeaxanthin) and hydrocarbon (the carotenes including beta carotene, and lycopene). The only carotenoids found in the eye (macula pigment) are lutein and zeaxanthin. Unfortunately, the hydrocarbon carotenoids compete for circulatory lipoprotein transport space with xanthophyll carotenoids, thereby lowering the chance of dietary or supplemental lutein and zeaxanthin from ever reaching the eye.³¹

Essential fatty acids

Because the body cannot produce essential fatty acids (EFAs), we must obtain them from diet. EFAs serve many functions, including production of pro- and anti-inflammatory prostaglandins.

Omega-3 and omega-6 fatty acids compete for the same metabolic enzymes, thus the ratio of each influence the production of site-specific prostaglandins (eicosanoids). Junk food diets (i.e. most processed foods) produce EFA ratios between 10:1 and 20:1, with the ratio dramatically skewed toward omega-6. The nutritional biochemists' recommended ratio is still 4 (omega-6):1 (omega-3), although fish oil marketers now claim the ratio should be 1:1.³² Eating clean (eliminating junk food intake) is a better way to correct the ratio than trying to balance the omega-6/omega-3 ratio with overconsumption of fish oil.

► Omega-6. These EFAs are important for the production of site-specific prostaglandins, such as PGE1 and PGE2, which are responsible for both anti-inflammatory and pro-inflammatory reactions. These reactions are vital when the body needs to mount an inflammatory response, such as clotting, fever induction or swelling. Omega-6 fatty acids can metabolize to the site-specific anti-inflammatory eicosanoid, prostaglandin E1 (PGE1). Researchers have found that these particular prostaglandins may reduce mucosal tissue inflammation (including ocular surface) as well as reduce the inflammatory process associated with meibomianitis and reduced lacrimal gland aqueous output.³³

► Omega-3. Important nutritionally, essential omega-3 fatty acids are: alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). These fatty acids are precursors to site-specific prostaglandin eicosanoids that reduce inflammation throughout the body, including the eyes.

You can synthesize the long-chain omega-3 fatty acids, EPA and DHA, from plant-based omega-3 fatty acid ALA, but EPA and DHA synthesis from ALA (think flax seed oil) isn't assured in the best of circumstances. Many external factors can inhibit this process, such as alcohol, aging, nutrient deficiencies, trans fats and elevated cholesterol. Studies of ALA metabolism indicate that the body converts less than 8% of dietary ALA to EPA, and converts 0% to 4% to DHA in healthy young men.³⁴ In healthy young women, the body converts approximately 21% of dietary ALA to EPA, and converts 8% to DHA.³⁴

The best source for EPA and DHA is cold water small fish, such as salmon and sardines. Cod Liver Oil is also a source of EPA and DHA, as well as vitamins A and D.

Armed with the basic knowledge of both the macro- and micronutrients, you now have the ability to answer your patient's questions regarding nutrition, examine nutrition as a causative factor and possible treatment for eye disease and improve your patient's overall health — all of which not only solidify you as the go-to eyecare practitioner, but a vital member of the healthcare team. OM

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