Why Some Dairy Products are More Closely Linked to Parkinson’s Disease

Parkinson’s is the second most common neurodegenerative disease after Alzheimer’s. Each year in the United States, approximately 60,000 new cases are diagnosed, bringing the total number of current cases up to about a million, with tens of thousands of people dying from the disease every year. The dietary component most often implicated is milk, as I discuss in my video Could Lactose Explain the Milk and Parkinson’s Disease Link?, and contamination of milk by neurotoxins has been considered the “only possible explanation.” High levels of organochlorine pesticide residues have been found in milk, as well as in the most affected areas in the brains of Parkinson’s victims on autopsy. Pesticides in milk have been found around the world, so perhaps the dairy industry should require toxin screenings of milk. In fact, inexpensive, sensitive, portable tests are now available with no false positives and no false negatives, providing rapid detection of highly toxic pesticides in milk. Now, we just have to convince the dairy industry to actually do it.

Others are not as convinced of the pesticide link. “Despite clear-cut associations between milk intake and PD [Parkinson’s disease] incidence, there is no rational explanation for milk being a risk factor for PD.” If it were the pesticides present in milk that could accumulate in the brain, we would assume that the pesticides would build up in the fat. However, the link between skimmed milk and Parkinson’s is just as strong. So, researchers have suggested reverse causation: The milk didn’t cause Parkinson’s; the Parkinson’s caused the milk. Parkinson’s makes some people depressed, they reasoned, and depressed people may drink more milk. As such, they suggested we shouldn’t limit dairy intake for people with Parkinson’s, especially because they are so susceptible to hip fractures. But we now know that milk doesn’t appear to protect against hip fractures after all and may actually increase the risk of both bone fractures and death. (For more on this, see my video Is Milk Good for Our Bones?.) Ironically, this may offer a clue as to what’s going on in Parkinson’s, but first, let’s look at this reverse causation argument: Did milk lead to Parkinson’s, or did Parkinson’s lead to milk?

What are needed are prospective cohort studies in which milk consumption is measured first and people are followed over time, and such studies still found a significant increase in risk associated with dairy intake. The risk increased by 17 percent for every small glass of milk a day and 13 percent for every daily half slice of cheese. Again, the standard explanation is that the risk is from all the pesticides and other neurotoxins in dairy, but that doesn’t explain why there’s more risk attached to some dairy products than others. Pesticide residues are found in all dairy products, so why should milk be associated with Parkinson’s more than cheese is? Besides the pesticides themselves, there are other neurotoxic contaminants in milk, like tetrahydroisoquinolines, found in the brains of people with Parkinson’s disease, but there are higher levels of these in cheese than in milk, though people may drink more milk than eat cheese.

The relationship between dairy and Huntington’s disease appears similar. Huntington’s is a horrible degenerative brain disease that runs in families and whose early onset may be doubled by dairy consumption, but again, this may be more milk consumption than cheese consumption, which brings us back to the clue in the more-milk-more-mortality study.

Anytime we hear disease risks associated with more milk than cheese—more oxidative stress and inflammation—we should think galactose, the milk sugar rather than the milk fat, protein, or pesticides. That’s why we think milk drinkers specifically appeared to have a higher risk of bone fractures and death, which may explain the neurodegeneration findings, too. Not only do rare individuals with an inability to detoxify the galactose found in milk suffer damage to their bones, but they also exhibit damage to their brains.


Other than avoiding dairy products, what can we do to reduce our risk of Parkinson’s? See Is Something in Tobacco Protective Against Parkinson’s Disease? and Peppers and Parkinson’s: The Benefits of Smoking Without the Risks?.

You may also be interested in my videos Treating Parkinson’s Disease with Diet and Parkinson’s Disease and the Uric Acid Sweet Spot.

For the effect of foods on another neurodegenerative disease that affects our ability to move normally, see ALS (Lou Gehrig’s Disease): Fishing for Answers and Diet and Amyotrophic Lateral Sclerosis (ALS).

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

Concerns About Bone Broth

There are toxicological issues associated with production and processing of meat, such as the presence of various toxic contaminants—from dioxins and PCBs to cooked meat carcinogens. Carcinogenesis, the development of cancer, may be the main concern, but there are a number of other toxic responses connected with the consumption of meat products. Lead, for example, can be toxic to the nerves, gastrointestinal tract, bone marrow, and kidneys.

Where is lead found in the food supply? In general terms, the highest levels of lead, as well as arsenic and mercury, are found in fish. Sardines have the most arsenic, but tuna may have sardines beat when it comes to mercury and lead.

The problem is that “fish-consumption advisories related to human health protection do not consider the fish by-products fed to farmed animals,” like farmed fish. If some tilapia are fed tuna by-products, they could bioaccumulate heavy metals and pass them onto us when we eat them. Researchers found the highest levels in frozen sole fillets, averaging above the legal limit for lead.

Lead exposure has been shown to have adverse effects on nearly every organ system in the body. Symptoms of chronic exposure range from memory loss and constipation to impotence and depression. These symptoms present after pretty hefty exposure, though. However, we now know that “[b]lood lead levels in the range currently considered acceptable are associated with increased prevalence of gout and hyperuricemia” (elevated levels of uric acid in the blood). According to the Centers for Disease Control and the World Health Organization, a blood lead level needs to be less than 25 micrograms per deciliter to be “non-elevated.” You’d assume that at values under 25, there’d be no relationship with health outcomes, but even throughout this “acceptable” range, lower lead means lower uric acid levels and lower gout risk. So, even blood lead levels 20 times below the acceptable level can be associated with increased prevalence of gout. “These data suggest that there is no such thing as a ‘safe’ level of exposure to lead.” 

Once lead gets into the body, it tends to stay in the body. It builds up in the bones such that it may take 30 years just to get rid of half. The best strategy? Don’t get exposed in the first place.

If lead builds up in bones, though, what about boiling bones for broth? As I discuss in my video Lead Contamination in Bone Broth, we know bones sequester lead, which can then leach from the bones. So, researchers suggested that “the bones of farmyard animals will sequester lead, some of which will then be released into broth during its preparation.” Who eats bone broth? Bone broth consumption is encouraged by many advocates of the paleo diet. Online, you can learn all about purported “benefits” of bone broth, but what they don’t tend to mention is the theoretical risk of lead contamination—or at least it was theoretical until now. Broth made from chicken bones was to have markedly high lead concentrations, up to a ten-fold increase in lead. Researchers concluded, “In view of the dangers of lead consumption to the human body, we recommend that doctors and nutritionists take the risk of lead contamination into consideration when advising patients about bone broth diets.”

But what if you only use bones from organic, free-range chickens? They did use only bones from organic, free-range chickens.


For more on the paleo diet, see:

Other products contaminated with lead include Ayurvedic supplements, protein powders, wild animals shot with lead ammunition, dairy products, and tea from China:

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

Should Plant-Based Women Supplement with DHA During Pregnancy?

A systematic review of randomized controlled trials of DHA supplementation of pregnant and breastfeeding women failed to find any clear and consistent short- or long-term benefit for psychomotor, mental, visual, or physical development. Perhaps DHA supplementation during pregnancy has no effect because the body wisely protects the growth of the baby’s brain by drawing off of maternal stores of DHA, upregulating maternal DHA synthesis, and preferentially shuttling it to the fetus. But what if moms don’t start out with large maternal stores? In other words, maybe DHA failed to help women who were already getting enough, but perhaps women with very low intakes would benefit from DHA supplementation. My video Should Vegan Women Supplement with DHA During Pregnancy? explores the evidence available to date.

It’s interesting to note that, by 1978, researchers already were suggesting a plant-based diet as the diet of choice in the treatment of our number-one killer, heart disease, but babies breastfed by vegan moms had significantly less DHA in their bloodstreams, presumably because the moms had significantly less DHA in their breast milk.

The question is whether these differences are of any consequence. The growth and development of vegan and vegetarian born children are normal as long as they’re getting their B12, and “[t]here is no evidence that neural or intellectual functions are impaired.” In fact, the two studies we have on kids in vegetarian communities showed they had higher IQs, though that may be because their parents tended to be better educated. However, even though the kids seemed fine, that doesn’t rule out the possibility that there may be some “subtle differences…in visual or neural functioning.”

It would be interesting to compare the function of babies getting vegan breast milk levels versus general population levels. In one of the studies I profile in my video, it shows that vegans hit a level of 14, vegetarians 30, and omnivores 37. Another study compared 0 to 32, 64, and 96, and, though 32 worked better than 0, more than 32 didn’t add anything. This could explain why the general population at 37 doesn’t benefit from additional DHA supplementation. But what about down at 14? Most studies at that level show no advantage over 0, though one study found a benefit supplementing at as low as 5, but that doesn’t help us.

Just because babies breastfed by vegan moms have significantly lower DHA levels in the blood, that doesn’t necessarily mean they have lower levels in their brain, which is where it counts. What we need is a randomized, controlled trial in non-fish-eaters of DHA supplementation. Until then, it’s going to remain uncertain. So, what should pregnant and breastfeeding women who avoid fish do in the meanwhile? Low intake of DHA doesn’t “necessarily equate with fetal DHA inadequacy,” but new data suggest that some infants may not be getting enough and could benefit from their moms supplementing. Given this, I recommend pregnant and breastfeeding women on plant-based diets to follow the consensus guidelines to get about 200mg of preformed DHA from an uncontaminated source, like algae oil, which is probably the best combination for all women given the state of our world to minimize exposure to toxic pollutants such as dioxins, PCBs, and mercury. 


To gain a better understanding of why algae oil is better than purified fish oil, I encourage you to watch my video Should Pregnant and Breastfeeding Women Take DHA.

I’ve discussed concerns about pollutants in seafood during pregnancy in a number of my videos:

Finally, for more on taking long-chain omega-3s to protect your heart, see: 

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations: