environmental toxins, air pollution
© istock / azgek
Toxins from our environment are ubiquitous and almost impossible to avoid. If you are taking steps to limit your exposure, should you be worried about the low levels that are still undoubtedly in your system? The answer is: it depends. Read on to find out how the traditional view of toxicity is outdated, what factors influence one's susceptibility to a toxin, and what else you can do to decrease your body's toxic burden.

We are exposed to thousands of environmental toxins, whether they are inhaled, applied to our skin, ingested with our food, or injected. Common exposures include substances found in:
  • health and beauty products, which I covered in a series of articles
  • pesticides and herbicides
  • industrial pollutants
  • mold
  • preservatives and flame retardants
  • petrochemical fuels and solvents
  • plastics and cookware
There is no denying that toxic chemicals are IN us. The Environmental Working Group (EWG) reported that the average person carries 91 toxic chemicals in his or her blood and urine. Another EWG study found 232 different toxins in the umbilical cord blood of 10 newborn babies. Do we fully understand how these chemical cocktails might be affecting our health?

Low doses of toxins can be harmful

Traditional studies for toxicity aim to find the lowest observed adverse effect level (LOAEL) and no observed adverse effect level (NOAEL). In other words, a level of a toxin that is known to cause harm is experimentally lowered until the toxic effects disappear. Toxicity studies usually test large doses to determine far-off endpoints like cancer and death, while ignoring small doses and subtle effects like endocrine disruption and immunotoxicity. Furthermore, most studies assume that everyone responds the same. No consideration is made for fetuses, young children, those in puberty, or people with chronic diseases.

However, a growing body of research indicates that chronic, low doses of many toxins can also be very harmful. Frogs that were given a mixture of nine pesticides at 10 to 100 times below EPA standard safe levels had slowed growth and higher levels of corticosterone and were more likely to be infected with a common pathogen, highlighting the shortcomings of regulatory studies that only look at an isolated chemical in large doses (1). In 2002, the National Toxicology Program reported adverse effects from low-dose exposure to common endocrine disruptors, including bisphenol A (BPA), genistein (an isoflavone derived from soy), methoxychlor (an insecticide), nonylphenol (an industrial chemical that can be found in drinking water), and vinclozolin (a fungicide), mostly in rodent studies (2). Ten years later in a large review, more adverse effects were confirmed for low doses of plasticizers, pesticides, phytoestrogens, industrial chemicals, preservatives, surfactants, flame retardants, and more (3). These researchers also explored how study design choices, such as animal strain selection and statistical methods, can skew results.cdx

Endocrine disruptors, which can mimic and interfere with the body's natural circulating hormones, are especially concerning (4). BPA is the endocrine disruptor that gets the most press, but a wide range of substances is continually being added to the list, including dioxins, PCBs, and some pesticides. When you look at BPA levels that have been found in human serum—we're talking nanograms per milliliter, which is analogous to less than a teaspoon of water in an olympic-sized swimming pool—they may appear too small to be significant (5). However, circulating blood estrogen levels in young girls are 100 times smaller, at under 15 picograms per milliliter. From this perspective, it is easy to see how very "low" doses of toxins can have huge effects when they far outnumber naturally circulating hormones.

Some toxins show different responses at high doses compared to low doses

Even more concerning is that low doses of a toxic substance can sometimes act differently in the body than high doses. For these chemicals, what happens to the body at high doses cannot be used to predict what will happen at low doses, a phenomenon called a non-monotonic dose response (6). Because regulation is designed to test a high toxic dose and keep decreasing it until the no observed adverse effect level (NOAEL) is found, many low-dose effects are completely missed and not reported.

Substantial evidence of non-monotonic effects has been found in everyday environmental toxins. In mice, fetal exposure to low doses of diethylstilbestrol resulted in prostate enlargement, but the opposite effect was found at high doses (7). Another mouse study showed that DEHP (a phthalate) increased fetal and maternal testosterone levels at low doses but not at high doses (8).

Effect differences at low and high doses have also been reported for many other common toxins, including BPA (9, 10), atrazine (an herbicide) (11), pyrethroid (an insecticide) (12), and more.

Toxicity susceptibility is highly individual

What determines "toxicity"? A variety of factors is important, including:
  • level of exposure
  • duration of exposure
  • frequency of exposure
  • synergistic relationships (chemicals together producing an effect that is more than additive)
  • timing (in utero, during puberty, while ill)
  • the least studied and understood of all, human variability
The liver is the major organ responsible for detoxification, a process divided into three phases. The first phase begins to process the toxins through oxidation, reduction, and/or hydrolysis (13). In Phase 2, conjugation pathways further break down the toxin byproducts into water-soluble compounds that can be excreted. Phase 3 involves cell membrane proteins that control the modified products' elimination (14). Sometimes, the products at the end of Phase 1 are more toxic than the beginning toxin, as with the conversion of ethanol (alcohol) to acetaldehyde. If Phase 2 isn't functioning properly due to nutrition deficiency or disease, toxic byproducts from Phase 1 can linger in the body with deleterious effects.

Susceptibility to toxicity is highly individual and dependent on one's ability to biotransform and excrete toxins through detoxification. Many factors can influence this process, and I am going to briefly summarize some of the research on several of them below.

Nutrition status and diet. Eating a variety of nutrient-dense, whole foods can help reduce the chances of toxicity. A 2014 review laid out the evidence that diets rich in fruits and vegetables, probably due to their innate antioxidant and anti-inflammatory properties, can help protect against environmental toxic stressors (15). Good intake of essential minerals reduced the uptake of heavy metals (16). Dairy products were associated with lower levels of lead from occupational exposure, possibly due to calcium - lead interaction (17). On the flip side, inflammatory diets, such as those high in omega-6 fatty acids, can increase the vascular toxic effects of PCBs (18).

Genetics. As with other body processes and disease progressions, genetic makeup can impact your body's detox ability. Even as early as 1985, researchers knew that chronic toxicity studies should include multiple strains of mice to account for genetic variations (19). In pharmacology, drug metabolism, which often occurs through detoxification pathways, is highly dependent upon genetics (20). Certain genetic variations, such as single-nucleotide polymorphisms (SNPs), can influence one's risk of toxicity following radiation therapy (21). Furthermore, being male vs. female can influence your toxicity susceptibility (22, 23, 24).

Gut health. As I have argued before, you're only as healthy as your gut. Research has shown that air pollution, heavy metals, and other toxins can all negatively impact the gut microbiome in mice and humans (25, 26, 27, 28, 29). In the pharmaceutical world, the gut is an important player in drug metabolism, efficacy, and toxicity (30, 31), and it looks like all those beneficial gut bacteria can help digest other toxic invaders, too. Probiotic supplementation reduced mercury and arsenic levels in pregnant women and children (32), and in a laboratory setting, probiotics were shown to decrease pesticide accumulation (33). Compared to "germ-free" rats, rats with normal gut microbiomes showed decreased toxicity to an herbicide (34).

Epigenetics. We now know that our DNA sequence doesn't determine everything about us. Epigenetics studies the different mechanisms that change how and when our genes are turned on or off, and some of these effects can be transgenerational. Epigenetics is one explanation for the differences in people's susceptibility to toxicity (35). Nematodes whose parents were exposed to silver showed 10 times increased sensitivity to this heavy metal, and these effects were present for 10 generations (36). BPA's effects on human fertility are also thought to be transgenerational (37).

Methylation. Methylation is a simple yet important biochemical reaction that occurs billions of times in our bodies. In liver detoxification, methylation is one of the conjugation reactions in Phase 2 that helps break down toxins (38). Glutathione, which requires methylation, is a major molecule in the detox cycle, especially in heavy metal detox (39, 40). If your methylation status is impaired, through genetics and/or lifestyle, your ability to detox can be similarly limited.

How to reduce your toxic burden

We know that even low levels of toxins can be harmful and that your body's individual ability to bioprocess and excrete toxins is difficult to fully assess. So what can you do? Some amount of exposure may be out of your control, but you can certainly strive for change:
  • Limit environmental toxins that are within your control. Be particular about which beauty, health, and other personal products you buy, and even consider making your own. Controlling room humidity can prevent indoor mold growth. Change any plastic food storage containers to glass or stainless steel, and use safer cookware. Consuming organic produce and animal products will greatly reduce your pesticide exposure. Consider installing a reverse osmosis water filtration system for drinking water and a filter for your shower head, as toxins can aerate when heated.
  • Improve liver detox. For liver detoxification to work properly, a wide variety of macronutrients, micronutrients, cofactors, and more is required. Milk thistle is commonly used to help support detoxification, and other supplements are also available. I recommend working with a functional medicine practitioner to help optimize any detox improvement protocol.
  • Improve gut health. If at all possible, avoid antibiotics, which can destroy the gut microbiome. Increase your intake of fermented vegetables like sauerkraut and, if tolerated, yogurt and raw dairy. Resistant starches like green bananas or cooked-and-cooled starchy tubers also boost gut health. And keep drinking that bone broth.

    Comment: Why Milk Is So Evil
    Dairy products can actually contribute to gut problems as there is no other food as difficult to digest as milk. Milk damages the intestinal environment, increasing the amount of bad bacteria and destroying the balance of the intestinal bacterial flora. As a result, toxins such as free radicals, hydrogen sulfides, and ammonia are produced in the intestine. These problems apply to all dairy products including, milk, cheese, cottage cheese, yogurt, kefir and ice cream.

  • Improve overall nutrition. Our bodies require nourishing, nutrient-dense whole foods as part of a Paleo lifestyle. Eliminate processed foods and refined sugars, which can increase inflammation and susceptibility to toxins