100 Million Years of Food (20 page)

Finland is a good place to check for a link between vitamin D deficiency and allergic rhinitis, because hours of sunlight there are scant and asthma rates are high. Researchers asked Finnish mothers who had given birth what they ate during their final month of pregnancy. When mothers acquired more vitamin D from food and supplements during their last month of pregnancy, their children had a lower chance of developing either allergic rhinitis or asthma.
28
This heightened impact of vitamin D on allergic rhinitis during a critical developmental window echoes the timing of the intake of omega fatty acids and the manifestation of allergic diseases.
29

Is the risk for developing food allergies also heightened by lack of vitamin D? Until recently, no one had a clue, in part because food allergies are defined differently in different places and studies of food allergies tended to focus on small populations. A breakthrough came in 2002, when researchers in Manitoba hit upon the idea of using EpiPen prescription data to study anaphylaxis rates. EpiPens are self-injectable devices that deliver an emergency dose of epinephrine (also known as adrenaline) in case of an allergy attack, the most common being food-induced anaphylaxis. In Canada and other countries, prescriptions are required to obtain EpiPens and related devices. Thus data on EpiPens gave researchers a detailed view for the first time on patterns of anaphylaxis. When doctors scoured American data on EpiPen prescriptions, they discovered that northeastern states had the highest rates of epinephrine prescriptions, while southwestern states had the lowest rates. The leader in anaphylaxis misery was snowy Massachusetts. The lucky losers in this competition? Who else but Hawaiians, with New Mexicans and Californians close behind.
30
The difference in EpiPen prescriptions between New England and other American regions remained true after controlling for possible differences between states in terms of factors such as age, sex, race, income, health insurance, and the number of allergists, pediatricians, adult primary care providers, and emergency physicians. A similar pattern emerged in Australia, where EpiPen prescriptions and anaphylaxis admissions among children were more frequent in colder states such as Tasmania.
31

Recently, scientists and doctors in the United States and Australia have announced findings that provide additional support for the vitamin D/food allergy hypothesis. Emergency department admissions for acute allergic reactions are more common in the frigid American Northeast than in the Southwest, and kids under the age of five living in Boston who were born in the fall or winter season, stretching from September to February (and therefore likely to be deficient in sunlight and vitamin D), are more likely to develop food allergies, particularly to peanuts. Gloomier Australian states have higher rates of prescriptions for hypoallergenic baby formula than sunny states, and kids living in those less-sunny states are also more likely to develop peanut and egg allergies (as well as allergic eczema).
32
Bottom line: Being born or growing up in a cold climate probably puts you at greater risk of developing asthma, food allergies, and eczema, particularly if you are darker-skinned or spend a lot of time indoors.
33

Climate therapy targeting eczema since the 1950s has seen well-heeled Europeans flocking to the Baltic Sea, the French Atlantic and Mediterranean coasts, resorts in the Canary Islands, and other temperate areas around Eastern Europe and Western Asia for relief. Though the efficacy of sunlight on eczema was undeniable, only in the past decade have scientific trials been carried out to test this effect. One of the pioneering studies was done in Boston, where kids who took vitamin D daily showed improvement in their eczema symptoms. (This was a very small study involving eleven children.) Researchers in Iran reported similar success with vitamin D treatment of eczema. In a study of Italian children with eczema, the severity of their symptoms varied in direct proportion to vitamin D levels.
34
In 2008, researchers at the University of California, San Diego, noted that people who had eczema produced more antimicrobial amino-acid chains known as cathelicidin in the diseased portions of their skin; taking vitamin D supplements greatly elevated production of protective cathelicidin amino-acid chains.

In the last seven years, scientists cracked the genes that underlie one kind of eczema, ichthyosis vulgaris (“fish-skin disease”). Around 9 percent of people of European ancestry, 7 percent of Singaporean Chinese, and 4 percent of Japanese carry a genetic mutation that prevents their skin from manufacturing properly functioning filaggrin (filament-aggregating protein), a protein that normally teams up with lipids to keep water, microbes, irritants, and allergens out of the body. Without filaggrin, the skin becomes dry, scaly, and itchy, and a person becomes more susceptible to allergic reactions through the impaired skin. No one has yet offered a good reason why genes that predispose people to eczema are so widespread. It has been suggested that a more permeable skin in people with only one copy of the mutated filaggrin gene could have enabled “natural vaccination” through enhanced exposure to low concentrations of infectious diseases like tuberculosis and influenza; two copies of the same gene cause severe eczema and would have been a disadvantage, but the mutated filaggrin genes persist in populations because of the advantage gained by people who only have one copy of this gene.

Alternatively, since eczema often disappears in hot humid weather, eczema may only be a factor in contemporary industrial societies where people spend a lot of time in buildings that are equipped with heating or cooling systems that produce dry air, and where hot showers that strip away the skin's oils are considered a mandatory part of everyday life. My mother and I were able to tolerate torrid summer heat more easily than the rest of our family, and we both disliked air-conditioning. There are many more variants of mutated filaggrin genes in hot humid Asia compared to European populations, supporting the idea that there has been longer evolutionary selection for more permeable skin in hot humid climates.
35

*   *   *

Our view of the effects of sunlight on health is rapidly expanding. This is both good and bad news. The good news is that our bodies are designed to tolerate and utilize a lot of sunlight, and therefore the details behind vitamin D, sunlight, and health are interesting but not crucial, as long as we receive adequate sunlight. The bad news, for people who avoid sunlight, or live in much hotter or colder regions of the world than their ancestors did, or work exclusively indoors, is that there is no quick fix for sunlight deprivation, such as taking vitamin D supplements. Although growing evidence seems to implicate vitamin D deficiency in causing allergic diseases, in a few studies, scientists have observed that more vitamin D means a
greater risk
of getting an allergic disease. For example, researchers analyzing survey data on 18,244 men and women across the United States found that white Americans who had higher levels of vitamin D were more likely to have been diagnosed with allergic rhinitis. Meanwhile, researchers poring over Finnish health records spanning three decades concluded that people who had received regular vitamin D supplementation (greater than 2,000 IUs, or international units, per day) in their first year of life had a greater likelihood of developing allergic sensitivities, allergic rhinitis, or asthma as adults. In Sweden, children who had more vitamin D from food and supplements were more likely to develop eczema. In England, mothers who had high levels of vitamin D in blood tests were more likely to give birth to children who developed eczema and asthma. Even more worrisome, researchers are observing that high levels of vitamin D seem to increase risks of esophageal, pancreatic, and prostate cancer in men. Frank Garland, one of the founding investigators and prominent boosters of vitamin D, died of esophageal cancer at age sixty.
36

Some vitamin D supporters have criticized these studies for weaknesses such as small sample sizes and failure to control for confounding variables such as additional items in the diet outside of the study period. Other researchers suggest that the real danger lies in excessively high dosages of vitamin D. An additional consideration in taking vitamin D supplements is that vitamin D is a hormone. Hormones control the timing of our physical development, behavior, and reproduction, and thus do not take kindly to efforts by humans to meddle with their operations. Take, for instance, the roller-coaster history of postmenopausal hormone replacement therapy. Lured by promises of relief of symptoms of menopause such as hot flashes and vaginal dryness, purported lowered risks of cardiovascular disease and hip fracture, and clever pharmaceutical innovation (combining estrogen plus progestin to reduce the risk of endometrial cancer), 90 million women in the United States took oral, transdermal, vaginal, and injectable estrogens in 1999, the heyday of postmenopausal therapy. Then, starting in mid-2002, a series of reports highlighted hazards such as increased risk of breast cancer and cardiovascular disease, causing a mass exodus from estrogen therapy and likely triggering a one-time 6.7 percent drop in U.S. breast cancer rates in 2003. Menopause is a biologically programmed cessation in reproduction, which seems to have evolved to spare ancestral women the danger of giving birth at a period when their existing offspring or grand-offspring were still highly dependent on them for survival (the hazard of childbirth is compounded in humans due to the constraints of narrow hips adapted for walking upright and the relatively large heads of human babies). We cannot easily or safely override this evolutionary imperative. The same can be said of other attempts at hormone manipulation, such as the use of human growth hormone to reverse aging in the elderly or doping with anabolic steroids for enhanced athleticism, both of which are now understood to carry substantial long-term health risks that outweigh their benefits.
37
Our bodies evolved to regulate vitamin D use through exposure to sunlight rather than vitamin supplements; circumventing this system by taking pills carries risks. The interaction of vitamin D with our bodies is too complex for scientists to guess at the proper dosage. This situation arises time and time again in the history of nutritional supplements. Hopes were raised and then dashed for beta-carotene, vitamin A, and vitamin E supplements, among others. This type of conflicting advice seems discouraging until one realizes that maintaining good health consists primarily of finding foods and lifestyles that reflect the conditions of our ancestors and then letting our bodies—exquisite products of millions of years of evolutionary refinement—do the rest of the work.

*   *   *

So far, we have discussed two of the three major hypothesized reasons for the increase in allergic diseases, omega-fatty-acids imbalance, and vitamin D deficiency. In the nineteenth century, observers in England noted that people who suffered from hay fever, or allergic rhinitis, came disproportionately from the upper classes, which raised the possibility that something about education or race was involved in the condition.
38
In 1966, researchers in Israel observed that the incidence of multiple sclerosis
increased
with better sanitation, such as cleaner drinking water, less crowding, and the availability of flush toilets. A major breakthrough came in 1989, when Professor David Strachan, a lecturer in epidemiology at the London School of Hygiene and Tropical Medicine, observed that children with older siblings in the same household had lower rates of hay fever and eczema. Now, if a researcher looks at a large database with many cases and many factors, some of those factors will coincide purely through chance, just as cloud or rock formations may resemble a dragon or horse. What made Strachan's study striking was that for each additional older sibling, there was a corresponding drop in the likelihood that a child developed hay fever or asthma, as if having siblings were medicine whose effectiveness increased with each older brother or sister. Such regularity in a trend is highly unlikely to arise by chance. To top it off, Strachan had an insightful suggestion for why this pattern existed: When children come down with illness, they get their siblings (and parents) sick as well. A history of infectious disease was somehow protecting children against developing allergic diseases in later life.
39

The “hygiene hypothesis” sparked resurgent interest in the connection between infectious and allergic disease. Scientists discovered that children showed improvement in symptoms or markers of allergic diseases if they:

• were not born via Cesarean section;

• owned a furry pet;

• attended day care;

• lived in a crowded household;

• were less frequently bathed or had their hands washed less frequently;

• were not vaccinated;

• received fewer antibiotics early in life;

• were exposed to bacterial toxins in mattresses;

• lived on farms;

• were exposed to farm animals;

• drank unpasteurized milk;

• had no access to sewage or clean water;

• were infected by viral diseases such as hepatitis A, herpes, or measles;

• were infected by noxious bacteria such as salmonella,
Helicobacter pylori
(induces inflammation of the stomach lining), or
Mycobacterium tuberculosis
(responsible for tuberculosis); or

• were infected by parasites or parasitic diseases such as malaria, giant roundworms, hookworms, flukes, pinworms, whipworms, or
Toxoplasma gondii
(usually infects cats, but can also be carried by rats and humans).
40

As with omega-3 and vitamin D, the earlier in life exposure to pathogens and toxins occurs, the greater the reduction in allergic disease tends to be. The first item on this list and possibly the second (furry pets and day care) are likely the only ones that many Western children have encountered. Other exposures help protect farm children from allergic diseases. The last four items will send a shiver down the spines of Western parents, but such conditions are the lot of most kids in the developing world and indeed of most humans throughout history until recently.