100 Million Years of Food (19 page)

Once the role of vitamins was understood, progress was rapid. Adding vitamins like B
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(thiamine), B
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(niacin), and D to factory-produced foods was straightforward; such measures required no alterations in habits, and because the vitamins could be produced cheaply, no one protested the additions. Moreover, the companies that produced the vitamins profited handsomely, and thus the disasters of beriberi, pellagra, and rickets were averted in the ways in which capitalistic societies operate most comfortably: with the scent of profit, the comfort of cheap goods, and minimal prodding from public authorities. Unfortunately, the scent of profit and the lure of quick vitamin fixes continues to dazzle the public: The U.S. supplement industry registered a strapping $28 billion in sales in 2010 despite a lack of evidence for benefits from taking vitamins and antioxidant supplements among today's well-nourished population.
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The lure of “superfoods” is similarly dubious.

Today, industrialized societies are facing several new epidemic diseases that are being studied for potential treatments; however, because the basis of these diseases conflicts strongly with past medical understanding of how the body works, there is a lot of conflict and confusion among medical experts and the public. We'll consider two paradigm-breaking clusters of diseases: sunlight-deprivation diseases and allergic diseases. It now appears that myopia (i.e., nearsightedness) and allergic diseases are triggered by radical lifestyle shifts that were undertaken in recent centuries and decades. Understanding myopia forces us to reconsider the role of sunlight in guiding the development of the eye, and reining in allergic diseases compels fresh thinking on hygiene and bacterial warfare, as well as the influence of sunlight and vitamin D on the immune system.

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From the point of view of evolution, nearsightedness is a great mystery. Back in hunter-gatherer times, anyone unable to spy a stalking predator or a tasty morsel in the forest would have been at a tremendous disadvantage. Myopia was first described by the ancient Greeks, but in the two thousand years since, no one has ever come up with a good explanation for why myopia developed in some people and not others. The old theory was that engaging in too many near-work activities, like reading or writing (or these days, using a computer or smartphone or playing with handheld video games), resulted in prolonged tension of eye muscles and eventually permanent myopia. This theory was proposed at least as far back as 1866 and seemed to make sense, since children first develop myopia during the early school years and myopia is more common among white-collar occupations and rises with education level. However, empirical studies show mixed results about the alleged effect of near work on vision, and the use of various types of lenses to correct for near-work effects have so far been unable to halt myopia from progressing in children. Meanwhile, the prevalence of myopia is rising in regions like East Asia. For example, in Singapore, the prevalence of myopia nearly doubled over a two-decade span, reaching 43 percent among young men.
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In striking contrast to the muddled empirical results of the near-work theory of myopia, in back-to-back studies in three different countries, children who play outside more frequently were found to be less nearsighted (Australia, the United States, and Singapore).
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The most solid explanation for this pattern is that sunlight is protective against nearsightedness. This pattern has been replicated in controlled experiments with chickens and monkeys, and also in a study that looked specifically at ultraviolet exposure and myopia. The reason sunlight helps prevent myopia could be the greater depth of focus and clearer retinal image achieved in bright sunlight or the stimulation of dopamine from the retina by sunlight. Sunlight's protective effect may help explain why myopia rates are lower in Europe than in East Asia: Blue eyes have very little melanin in the iris compared to brown eyes and hence may permit greater intensity or different wavelengths of light to impact the pupil. Additional studies will be required to develop a complete account of the mechanics underlying myopia, but in the meantime, some people will find ways of increasing lighting inside homes so that it more closely mimics the tremendous intensity of natural sunlight; conversely, they could opt to let their kids play outside more.
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In addition to lowering the risk of nearsightedness, bright light triggers serotonin production in the human brain and combats the misery of seasonal affective disorder (SAD) and depression. Among patients admitted for treatment of depression at a Canadian psychiatric ward, those who by chance received one of the sunny east-facing rooms checked out of the hospital nearly three days sooner than those who were allotted one of the dimmer rooms. The antidepressive effects of sunlight may go beyond shortening hospital stays: Among patients admitted to the cardiac intensive care unit for heart attacks, those who stayed in one of the dim rooms had a higher chance of dying than those who received one of the sunny rooms. Over a four-year stretch, 13.2 percent of the patients who stayed in one of the four dim north-facing rooms died, compared to 7.7 percent of those who received one of the four sunny south-facing rooms.
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Sunlight or geographical latitude effects have also been noted in the incidence of schizophrenia and autism, ailments that have befuddled researchers up until now. Colder northern countries have the heaviest burden of each of these diseases (and in the case of schizophrenia, children of darker-skinned immigrants are particularly susceptible), leading researchers to investigate whether melatonin disruption, vitamin D deficiency, or some other factor is causing the association of these diseases with paucity of sunlight.
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Left to its own devices, the skin regulates production of vitamin D from ultraviolet light (UVB, to be specific) to manageable levels, just as our body does with all our other hormones. However, there are two major problems with relying solely on our skin to provide vitamin D. First, there's the problem of our beautiful birthday suits. Human skin pigmentation evolved over thousands of years to provide the optimal balance of vitamin D production, protection against cancer-inducing ultraviolet light, and protection against damage to folate levels (folate, or vitamin B
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, is easily damaged by ultraviolet radiation). When humans migrated out of Africa into Europe and East Asia, skin types in these latter two regions independently evolved to become lighter, powerful evidence that sunlight was an important factor influencing mortality. However, you can't change skin color like a coat, so when Europeans started to populate sunny colonies in the Americas and Oceania beginning a few hundred years ago, and people from the tropics, like my parents, moved in the opposite direction, to frigid climes, the wonderfully adapted skin color suddenly became a liability. My Caucasian friends get sunburn from the Californian, Australian, and Southeast Asian sun, while my tropical immigrant friends and I languish from sunlight deficiency in northern cities like Ottawa, Umeå, and Sapporo.
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The second problem with relying on skin for our vitamin D is our pattern of sun exposure. Some people are able to tan, which is the skin's method of adapting to the rise and fall of ultraviolet rays over the seasons. These days, when sun-starved office workers dash outside to play on weekends, then spend the rest of the week working inside, the alternation between scorching and seclusion sets us up for increased risk of sunburn and developing cutaneous melanoma, the most aggressive form of skin cancer. To avoid skin cancer, people slap on sunscreen, but it's unclear whether this practice helps or harms, since sunscreen may give people a false sense of security and encourage them to spend more time outside, and the pattern of sunscreen wearing off and then being reapplied may exacerbate the dangerous intermittency of sun exposure. On top of that, the depletion of the ozone layer may be increasing our exposure to ultraviolet radiation beyond the range that our skin is adapted to handle. (Ozone pollution in big cities may cause the opposite effect and screen out UV light from reaching us.)

Not surprisingly, many people, for cultural or health reasons, decide to forgo the hazards of ultraviolet radiation altogether by seeking refuge under parasols, long-sleeved clothing, or heavy sunscreen use, but then they suffer from vitamin D deficiency, and we're back to square one. Others worry about vitamin D deficiency and pop vitamin D pills, but the problem is that no one knows exactly how much vitamin D is a healthy dosage or how vitamin D supplements influence our immune system and increase our risk for diseases like cancer. In my own case, I love Canada, especially during the quiet, languid summers, but the mismatch between my skinny brown body and the rigors of a Canadian winter is so uncomfortable that I spend as much time in the tropics as my schedule and meager budget allow.
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Most allergic diseases were unheard of only decades ago. In the West, there were two waves of allergies. Asthma initially surfaced fifty years ago and reached its highest rate in the 2000s. Hot on its heels, food allergies have besieged Western countries. In one of the most ambitious screening tests for food allergies yet conducted, more than 10 percent of infants in Melbourne were shown to have a food allergy to either peanuts, eggs, or sesame seeds, a higher rate than pediatricians and scientists had previously suspected.
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In Asia, rates of asthma are now rapidly rising, and it is expected that food allergies and eczema will arrive soon afterward. Curiously, some kinds of foods that trigger allergic reactions in Asia are turning out to be rather novel. For instance, in Singapore, the most common trigger of anaphylaxis (the rapid onset of severe allergic symptoms, including hives and difficulty in breathing) is edible bird's nests, a Chinese delicacy made from the saliva of cave swifts. Buckwheat is a common allergen in Japan, while the same is true of chestnuts in South Korea and chickpeas in India. As in the West, eggs, milk, and sesame are also commonly reported to induce allergic symptoms.
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Why is the allergy epidemic rearing its ugly head now, and what can be done about it? Scientists have analyzed three large-scale changes in traditional diets and lifestyles that are suspects in the allergy epidemic. The first is the shift in the human diet in industrialized countries from inflammation-calming omega-3 fatty acids to inflammation-inciting omega-6 fatty acids. This dietary transformation resulted from feeding livestock with seeds like corn, instead of allowing them to indulge in their natural diets of grasses or insects, from the widespread use of processed seed and vegetable cooking oils, and from reliance on industrially produced foods instead of harvesting wild plants and animals. A number of recent studies have scrutinized the relationship between childhood allergic diseases and consumption of omega-3 and omega-6 fatty acids. Babies born to mothers who took fish-oil supplements show fewer allergic symptoms to cat allergen and egg than babies born to mothers who took olive oil supplements.
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Children who eat more fish in early life have lower risks of asthma, eczema, allergic rhinitis (commonly called hay fever, though allergic rhinitis includes allergies to more than just hay), and produce fewer antibodies in an allergen blood test.
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Children whose mothers had a history of asthma but who ate oily fish at least once a month during pregnancy had a lower incidence of asthma. On the other hand, if their mothers were fond of eating fish sticks during pregnancy, the kids had a higher risk of developing asthma. Fish sticks are made from cod or pollock, which have low levels of omega-3 fatty acids. Moreover, American fish sticks are only 40 percent to 72 percent fish flesh by weight, and the batter coating is made from fried corn, canola, cottonseed, and soybean oil, which are heavy in inflammatory omega-6 oils. To make matters worse, when these oils are heated to high temperatures, they transform into trans-fatty acids, which are notorious for increasing inflammation.
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Much the same result was obtained in a German study: If mothers ate margarine or vegetable oil (both high in inflammatory omega-6 fatty acids) during their final month of pregnancy, their children were more likely to develop eczema by two years of age. If mothers ate fish in the final month of pregnancy, their children were less likely to develop eczema, as one would expect if omega-3 fatty acids truly help to reduce allergic diseases.
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While the logical arrows and evidence pointing from inflammatory omega-6 and transfat-rich foods to allergies seem straightforward, so far omega-3-rich diets have not been proven to be a magic wand for banishing allergic symptoms, at least for adults. A reasonable conclusion is that what your mother ate or what you ate as a child may be the key, rather than your best efforts later on in life, at least as far as omega-3/omega-6 modification is concerned. Pediatricians currently recommend mothers breastfeed up to four or six months of age to minimize the risk of infants developing allergic disease. Good to know, but not much help for the average Joe or Jane dreading the arrival of hay fever season.
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A second major set of theories about the allergy epidemic centers on the role of vitamin D. This interest developed in part because vitamin D receptors are found in nearly all immune system cells and because many immune system diseases have been observed to increase the farther one gets from the equator. Vitamin D deficiency has been studied in connection with asthma, allergic rhinitis, food allergies, and eczema.
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Asthma afflicts around 300 million people worldwide. Higher levels of vitamin D in the blood of children have been associated with lower rates, or better control, of asthma. Mothers with higher intake levels of vitamin D give birth to children who have lower rates of wheezing (a symptom often associated with asthma).
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