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MedPage Today [full article here] drew my attention to a recent Harvard study published in the journal Neurology [abstract here] which took a closer look at previously identified associations between dairy products and Parkinsons Disease. Their analyses were based on data from two large prospective cohort studies, the Nurses’ Health Study (n = 80,736) and the Health Professionals Follow-up Study (n = 48,610), with a total of 26 and 24 years of follow-up, respectively. An previous study (see below) found an increased risk of Parkinson’s with higher levels of dairy protein consumption.
The latest study looked more carefully at the different types of dairy product. They found that among those who ate 3 or more portions of low fat dairy per day (skimmed milk, low fat cheese and yogurt etc) 4 in 1000 went on to develop Parkinson’s disease, whereas among those who ate no portions of low fat dairy only 3 in 1000 developed the disease.
Comparing the two groups that equates to a roughly 33% increased relative risk. Of course that is only a rather piffling 0.1% absolute risk increase – hardly anything to worry about in the grand scheme of things. What makes this study interesting, however, is that the association did not exist for full fat dairy products only low fat ones.
Uric acid and Parkinson’s disease
The study’s authors speculate that the increased risk seen in the low fat milk group may be due to the ability of milk protein (casein and lactalbumin) to reduce uric acid levels. Parkinson’s disease and uric acid? I wasn’t aware of this link, so started digging into the research…
A particularly helpful review in Practical Neurology [Uric Acid’s Relationship with Stroke and Parkinson’s Disease: A Review] filled me in on the background.
It turns out that there is a growing body of evidence demonstrating an association between low uric acid levels and incidence of Parkinson’s disease. Not only do Parkinson’s sufferers tend to have have low levels of uric acid, but those with higher levels have slower and less aggressive progression of the disease. Importantly, some studies have identified that low uric acid levels four years prior to the onset of Parkinson’s symptoms has a stronger association than levels at onset of symptoms, suggesting that uric acid is linked to the pathogenesis of Parkinson’s.
Uric acid BTW is an intriguing endogenous antioxidant which although primarily synthesised by the body is also influenced by diet. Excess levels can lead to the formation of crystals which is the basis of the painful condition gout, but can also contribute to kidney stones and kidney damage. Foods containing purines, such as shellfish, offal, meat and beer, can raise uric acid levels, as can alcohol and fructose, so should be avoided if you suffer from gout or kidney stones. The idea that such foods may be protective against Parkinson’s is interesting (although clearly one would not want to go as far as to cause gout!) On the other hand, dairy, cherries and vitamin C are associated with lower risk of gout and are classed as hypouricemic foods as they reduce uric acid levels.
It is believed that uric acid may exert a neuro-protective effect through it’s antioxidant action:
It has been hypothesized that uric acid reduces oxidative stress on neurons. This may have a significant bearing on therapeutic management of disease, as many neurological disorders are believed to result from oxidative stress. As a potentially modifiable risk factor, the prospect for uric acid and its derivatives to play a role in disease modification or prevention has great potential. – Pello et al, 2009
Studies looking at dietary associations with Parkinson’s disease have identified that uric acid lowering foods (e.g. dairy) are always associated with an increased risk of Parkinson’s, except for one. Vitamin C is the only uric acid lowering nutrient associated with reduced Parkinson’s risk: possibly because it is a powerful anti-oxidant itself.
Full fat dairy
In the new study the increased risk for Parkinson’s disease was only associated with low fat dairy, not full fat. Why wasn’t full fat dairy associated with an increased risk of Parkinson’s?
For now there is no clear answer, but according to MedPage Today the authors of the study say “The lack of association with full-fat dairy products could be due to a countervailing effect of saturated fats. I think more research is needed to better understand the mechanisms involved in this association,”
The benefits of dairy fats have come up time and again, yet I still know many people who avoid full fat milk, cream, cheese and butter. See our posts:
- Children who drink skimmed milk more likely to become overweight
- Full fat dairy consumption linked to reduced central obesity in Swedish men
- Brazil: “for each additional serving of full-fat dairy products people consumed, their risk for having metabolic syndrome decreased by 13%”
- Full fat cheese improves HDL cholesterol more than low fat cheese
- Review identifies that saturated fats, especially in dairy can improve health.
The size of the increased absolute risk of Parkinson’s disease associated with consuming low fat dairy products (0.1%) is too small to make it a reason in and of itself to avoid low fat dairy – unless of course, you have a family history of the disease in which case every bit of risk reduction helps.
For all of us, however, this study adds to the evidence of the benefits of full fat over low-fat dairy.
- Intake of dairy foods and risk of Parkinson disease, Katherine C. Hughes et al, Neurology, June 2017 [Abstract]
- Low-Fat Dairy Linked to Small Increased Risk for PD, Full article] Contributing Writer, MedPage Today, June 2017 [
- Uric Acid’s Relationship with Stroke and Parkinson’s Disease: A Review Scott Pello et al, Practical neurology, Jul/Aug 2009 [Full article]
- Diet, Urate, and Parkinson’s Disease Risk in Men, Xiang Gao et al, American journal of epidemiology, 2008 [PMC full text]