Vitamins

Inadequacy of Carbohydrates, Fat, Protein, and Minerals Alone

The enervation of rats fed pure carbohydrates, fat, protein, and minerals in the early twentieth century implied that such diets lacked an unknown nutrient or nutrients. The search for this substance or substances—what British biochemist Frederick Gowiand Hopkins (1861-1947) in 1912 termed “unsuspected dietetic factors”—involved scientists and physicians in Asia, Europe, and North America.⁷⁶ That year Polish biochemist Casimir Funk (1884-1967) invented the term “vitamine,” now spelled without the “e,” for Hopkins’ factors.⁷⁷ Its root is the Latin vita, meaning “life.” The original spelling conveyed the initial but incorrect belief that all vitamins had an amine group characteristic of amino acids and proteins. During the twentieth century, researchers named thirteen to sixteen vitamins— depending on which are counted as such—classifying them by whether they dissolved in water or fat.⁷⁸ Unlike carbohydrates, fats, and proteins and like minerals, the body needs vitamins in only small quantities. Fractions of a gram suffice and superabundance may harm the body. Vitamins resemble the macronutrients in being organic and often benefit specific metabolic pathways. In cases where effects are additive, shortage or absence of one vitamin disables or diminishes another.

Fat-Soluble Vitamins

Scientists ordered vitamins by letter, with the first discovery receiving “A”. The fat-soluble vitamins—A, D, E, and К—are in the fatty parts of plants, animals, and animal products. Fat-free foods cannot contain them. The body cannot absorb them unless it consumes some fat and can store them only in adipose and fatty structures within other cells. Because these vitamins do not dissolve in water, the body cannot excrete them in urine. Storage poses risk of superabundance, which, although uncommon, can harm the body. Vitamins A and D display greatest potential for injury in excess.

Taking the fat-soluble vitamins in order, A aids vision, cell growth, and the immune system. Animal products contain this vitamin in complete form, though the body can manufacture it from plant compounds known as carotenoids, which are vitamin A precursors. A later section examines these molecules, beta carotene prominent among them. Vitamin A is in eggs, dairy, the liver of various animals, and fish. Red and yellow vegetables and fruits contain carotenoids. This category includes carrots, red peppers (Capsicum annuum), tomatoes, apricots (Primus armeniaca), peaches (Primus persica), and mangoes (Mangifera indica). Additionally, dark green leafy vegetables and broccoli have carotenoids. The National Research Council of the National Academies of Sciences, Engineering, and Medicine in Washington, DC, having established the recommended dietary allowances (RDA) for nutrients, urges men to consume 900 micrograms (meg) of vitamin A and women 700.⁷⁹

Discussed in Chapter 1 and a previous section, vitamin D is atypical because the body can manufacture it independent of food. For this reason, Canadian biochemist Glenville Jones disputed its designation as a vitamin, instead terming it a “nutritional entity.”⁸⁰ Curiosity about the relationships among sunlight, skin, and pigmentation and between sunlight and bone health contributed to understanding vitamin D’s synthesis and functions. Sunlight’s benefits were apparent before the 1910s, when nutritionists and dieticians began recommending consumption of cod liver oil to combat rickets and osteomalacia.⁸¹ Considered from nutrition’s vantage point, vitamin D is in egg yolks, liver, fish oils, veal, beef, and fortified foods like dairy products. The RDA is 10-20 micrograms, or 400-800 international units (IU), depending on age and on pregnancy and lactation for women.⁸²

Vitamin E (tocopherol) is an antioxidant, a class of compounds whose benefits a later section describes. Tocopherol stabilizes LDL, whose function was noted. Vitamin E aids red-blood-cell formation and helps the body store vitamins A and К and minerals iron and selenium. Tocopherol is in vegetable oils, peanuts, nuts, spinach, broccoli, and fortified products like breakfast cereals and margarine. The RDA is 4-15 milligrams (mg) or 6-22.4IU depending on age and on pregnancy and lactation for women.⁸³ Because natural sources are best, people who consume vitamin E in fortified products should aim for 33 IU per day. Superabundance does not appear to harm the body.

Vitamin К activates the protein cascade necessary to clot blood in a wound and strengthens bones by binding calcium to proteins in them. Vitamin К is a broad designation for the compounds phylloquinone (K,), menaquinone (K₂), and menadione (K₃), which share properties and tend to occur in leaves. Good options are dark green leafy vegetables, broccoli, cauliflower, soybeans and their products, green tea, and wheat bran. Animal sources include liver and fermented dairy products. Laboratories synthesize menadione, whose potential harm diminishes its suitability in nutritional supplements. Vitamin K’s RDA is 90 micrograms for women and 120 for men.⁸⁴ Diets are seldom deficient.

Water-Soluble Vitamins

Unlike their fat-soluble counterparts, the В vitamins and C, dissolving in water, tend to store poorly in the body due to excretion in urine and must be consumed regularly. Rather than storage in the manner of fat-soluble vitamins, the В complex and C congregate with enzymes whose function they enhance. Care must be taken in preparing foods with these vitamins, which may be lost through cooking and exposure to air and light.

Nutritionists and dieticians concentrate on eight В vitamins: B, (thiamine or thiamin), B₂ (riboflavin), B₃ (niacin or nicotinic acid), B₅ (pantothenic acid), B₆ (pyridoxine), B₇ (biotin), B₉ (folate, folic acid, or pteroylmonoglutamic acid), and B₁₂ (cobalamin). The omitted four are B₄ (adenine), B₈ (inositol), B_l0 (para amino benzoic acid or PABA), and B_n (salicylic acid). This book concentrates on the standard eight. В vitamins help the body derive energy from food and manufacture red blood cells. As coenzymes, В vitamins enhance enzymes, a noteworthy function given that vitamins are not proteins and so cannot be enzymes. An example of a coenzyme, vitamin B, is part of nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), both necessary for deriving energy from foods. В vitamins are in beef, fish, poultry, eggs, dairy products, dark green leafy vegetables, and legumes. B-vitamin deficiencies cause diseases examined below.

The remaining water-soluble vitamin, C, receives attention elsewhere. Chapter 3 treats it from an evolutionary perspective. This paragraph restricts commentary to the publicity that American chemist and two-time Nobel laureate Linus Carl Pauling (1901-1994) garnered the vitamin by promoting it against the common cold. This belief generated controversy and the questionable practice of consuming large amounts (megadoses) of vitamin C in hopes of averting illness.

Vitamin Deficiency Diseases

The histories of scurvy, rickets, and osteomalacia, referenced earlier, indicate that attempts to fight deficiency diseases brought vitamins to the fore. Some ailments, known for thousands of years, defied solution until scientists isolated vitamins in the twentieth century. For example, the Chinese, Egyptians, and Greeks documented the failure of vision in poor light, a condition known as night blindness or nyctalopia.⁸⁵ Greek physician Hippocrates (c. 460-c. 375 BCE)—medicine’s putative founder, though several authors wrote his texts—is thought to have recommended liver’s consumption. In contrast to his recommendation, Egyptians, Indians (not American Indians), and Chinese put liquid from liver into the eyes. Japanese urged ingestion of fish oils and bird livers. As with scurvy, scientists sought the compound effective against nyctalopia common to these treatments. Vitamin A’s 1912 discovery provided the answer.

B-vitamin shortages cause at least three diseases. Beriberi, which may weaken the heart, circulation, muscles, and nerves, persisted among people whose staple was white rice. (All cultivated rice is in the genus Oryza and receives treatment in Chapter 12.) Restoration of rice bran, present in whole-grain rice, cured the disease. Success was due to vitamin B„ discovered in 1910 and named a vitamin in 1926. Pellagra resisted cure, Chapter 1 noted, until it was conceived not as a skin affliction but as nutritional shortfall. Suspicion fell on corn (Zea mays), which fed several peoples including blacks and poor whites in the southern United States. Attempts to blame the disease on corn’s deterioration in storage led nowhere. Only vitamin B₃’s discovery in 1937 and fortification of cornmeal and other foods cured pellagra. Anemia may result from deficiencies in B₉ or B₁₂. Anemia may also stem from inadequate iron or dearth of both iron and B₉ or B_l2. When both iron and a В vitamin are culprits, neither deficit need be large to cause anemia. Chapter 1 detailed these factors and anemia’s nondietary causes.

The battle against deficiency diseases spurred governments to mandate foods’ fortification. These efforts have produced milk with vitamin D; breakfast cereals, pasta, and breads with several vitamins and minerals; juices with vitamin C; rice and some vegetable oils with vitamin A; iodized salt; eggs with omega-3 fatty acids; soybean foods with calcium and vitamins A and D; and snacks with calcium. Those who want more nutrients may take supplements as pills, beverages, or powders. Some products contain a single nutrient whereas others supply several. Supplements may target men, women, children, or seniors. The consensus holds that supplements are less nourishing than whole foods.

Phytochemicals

The observation that plant eaters tend to be healthier than those who favor animal products implies that plants must contain compounds, known as phytochemicals or phytonutrients, that confer benefits beyond those available in carbohydrates, fat, protein, minerals, and vitamins and beyond what meat and kindred items supply.⁸⁶ This book eschews the term “phytonutrient” absent consensus about nutritional status. Phytochemicals’ novelty as research subjects cautions against generalizations, particularly because findings have been ambivalent and occasionally contradictory and counterintuitive. More scrutiny is necessary to untangle their effects.

Yet pessimism and circumspection are unnecessary in all cases. The subject of ongoing research, beneficial phytochemicals appear to be numerous in vegetables, fruits, legumes, and whole grains. Phytochemicals may be conspicuous, giving carrots, tomatoes, and other vegetables and fruits their distinctive appearance and enhancing aroma and flavor in onions, leeks (Allium ampeloprasum), garlic (A. sativum), chives (A. schoenoprasum), kurrat or wild leek (A. ampeloprasum), and shallots (А. сера). Chemical structure shapes attributes and functions.

Structure divides phytochemicals into five classes. The largest polyphenols includes flavonoids, which impart color to plant parts as mentioned, likely an adaptation for attracting insects to pollinate flowers. Flavonoids in legume roots attract nitrifying bacteria. More generally, flavonoids may protect plants against pathogens and help transmit intracellular and extracellular messages. In the body, flavonoids are antioxidants, which appear to protect cells against free radicals. Free radicals are electrically neutral, reactive atoms or molecules.

Consider hydrogen, the simplest atom. It has a single positively charged proton in the nucleus. To retain electrical neutrality, hydrogen has one negatively charged electron to counterbalance the proton’s positive charge. This single electron occupies what chemists and physicists term the lowest orbital or shell, which is stable with two electrons rather than one. Consequently, hydrogen reacts with other atoms or ions to achieve a full lowest orbital of two electrons. Free radicals may damage cells by bonding with proteins, membranes, and DNA in a type of electron theft known as oxidation. Such damage may make cells cancerous. Antioxidants protect cells by donating electrons to free radicals, thereby preventing them from scavenging electrons. Antioxidants may protect the body against pathogens, inflammation, and heart disease.

A second category, phytoestrogens, includes isoflavones, which appear to protect the body against heart disease, osteoporosis, and some cancers. Soybeans have the isoflavones genistein and daidzein, which may partly explain lower chronic-disease rates among East Asian than among Americans and Europeans. Another type of phytoestrogen, lignan, may offer comparable benefits and is numerous in flaxseeds (Linum usitatissimum). A third class of phytochemicals, phytosterols, resembles cholesterol and appears to lower it in blood. Soybean oil contains phytosterols, another factor that may help explain East Asians’ health. Fourth, glucosinolates may reduce damage from carcinogens and toxins by speeding their excretion, though clinical trials have yet to confirm this effect. Research focuses on glucosinolates sinigrin and progoitrin in hopes of evaluating their promise. These compounds are abundant in crucifers (also known as cole crops): broccoli, cauliflower, turnip (Brassica rapa ssp. rapa), kale, Brussels sprouts, garden cress (Lepidium sativum), bok choy (Brassica rapa ssp. chinensis), cabbage, and related plants. Fifth, the carotenoids include some 600 chemicals, notably vitamin A precursor beta carotene.⁸⁷

Other carotenoids are less valuable in this regard. Beta carotene is thought to protect the body against heart disease, though clinical results are disappointing. A 1996 study yielded higher rates of lung cancer and heart disease among smokers who ingested beta carotene than among smokers who did not.⁸⁸ Beta carotene’s potential harm may stem from its antioxidant properties. Because they donate electrons, beta carotene and other antioxidants may become free radicals capable of the damage outlined above. Resembling beta carotene, lycopene, plentiful in tomatoes, may protect against heart disease, stroke, and prostate cancer. Other sources are watermelon, pink grapefruit, guava (Psidium guajava), and apricots.