In an effort to better understand Parkinson’s, researchers have repeatedly analysed data from large epidemiological studies in order to gain insight into factors that could have a possible causal influence in the development of the condition.
This week a manuscript was made available on the preprint website BioRxiv that provided us with a large database of information about aspects of life that are associated with increased incidence of Parkinson’s.
Some new associations have been made… and some of them are intriguing, while others are simply baffling!
In today’s post, we will have a look at what has been learnt from epidemiological research on Parkinson’s, and then discuss the new research and what it could mean for Parkinson’s.
What are the differentiators? Source: Umweltbundesamt
What makes me different from you?
Other than my ridiculous height and the freakishly good looks, that is. What influential factors have resulted in the two of us being so different?
Yes, there is the genetics component playing a role, sure. 7,500 generations of homo sapien has resulted in a fair bit of genetic variation across the species (think red hair vs brown hair, dark skin vs light skin, tall Scandinavians vs African pygmies, etc). And then there are aspects like developmental noise and epigenetics (factors that cause modifications in gene activity rather than altering the genetic code itself).
And over-riding all of this, is a bunch of other stuff that we generally refer to simply as ‘life’. Habits and routines, likes and dislikes, war and famine, etc. The products of how we interact with the environment, and how it interacts with us.
But which of all these factors plays a role in determining our ultimate outcome?
It is a fascinating question. One that absorbs a large area of medical research, particularly with regards to factors that could be influential in causing a specific chronic conditions.
What does this have to do with Parkinson’s?
Here’s a good riddle for you:
Many epidemiological studies have suggested that coffee/caffeine consumption reduces one’s risk of developing Parkinson’s. Study after study has suggested that drinking coffee is beneficial.
Recently, however, Japanese researchers have discovered something really curious: people with Parkinson’s have reduced levels of caffeine in their blood compared to healthy controls… even when they have consumed the same amount of coffee. (???)
In today’s post we will look at what coffee is, review the results of this study, and try to understand what is going on.
Kaldi the goat herder. Source: CoffeeCrossroads
Legend has it that in 800AD, a young Ethiopian goat herder named Kaldi noticed that his animals were “dancing”.
They had been eating some berries from a tree that Kaldi did not recognise, but being a plucky young fellow – and being fascinated by the merry behaviour of his four-legged friends – Kaldi naturally decided to eat some of the berries for himself.
The result: He became “the happiest herder in happy Arabia” (Source).
This amusing encounter was apparently how humans discovered coffee. It is most likely a fiction as the earliest credible accounts of coffee-consumption emerge from the 15th century in the Sufi shrines of Yemen, but since then coffee has gone on to become one of the most popular drinks in the world.
Silly question, but what exactly is coffee?
We have previously written about the enormous contribution that the ‘Honolulu Heart Study’ has made to our understanding of Parkinson’s disease. This longitudinal study of 8006 “non-institutionalized men of Japanese ancestry, born 1900-1919, resident on the island of Oahu” has provided some with amazing insight to this condition by allowing us to go back and look at what variables were apparent before people were diagnosed with Parkinson’s disease (Click here to read that post).
Earlier this year, some researchers associated with the study reported an interesting observation.
It involved milk.
In today’s post, we’ll discuss what milk might taught us about Parkinson’s disease.
United Providers of Milk. Source: RSPB
In essence, milk is a pale liquid extracted from the mammary glands of mammals.
Riveting stuff, huh?
Ever since glandular skin secretions began with the evolutionary precursors to mammals – the synapsids – milk has remained the primary source of nutrition for infants. In addition to providing sustenance during early life, however, milk also contains colostrum which transfers elements of the mother’s own immune system (specifically antibodies) to the offspring. This exchange gives junior some extra help in strengthening their own developing immune system.
The synapsids family – proto mammals. Source: Feenixx
As infants grow, there is the process of weaning which gradually introduces the infant to a proper diet and reduces the need for the mother’s milk.
A proper diet. Source: Huffington Post
Now this basic idea of milk sustaining and aiding infants worked just fine until about 10,000 years ago, when we humans began doing something rather different:
We began drinking the milk from other mammals.
Sounds disgusting when you write it like that, I know, but between 7000-9000 years ago in south west Asia humans began drinking a lot more milk. Initially sheep’s milk, as it wasn’t until the 14th century that cow’s milk actually became more popular. But today there are more than 250 million cow producing milk for a dairy consuming population of over 6 billion people (despite the fact that milk can be be made in a laboratory – read more here: Cow-less milk).
Drinking milk certainly has it’s benefits:
- one of the best sources of calcium for the body.
- filled with Vitamin D that helps the body absorb calcium.
- contributes to stronger and healthier bones/teeth
But have you ever considered whether there is any downside to drinking milk?
Because there are.
For example, drinking too much milk can impair a child’s ability to absorb iron and given that milk has virtually no iron in it, this can result in increased risk of iron deficiency.
And then, of course, there is that thing that the Honolulu Heart Study told us about milk and Parkinson’s disease.
What did the Honolulu Heart Study tell us about milk and Parkinson’s disease?
The Honolulu Heart Study – a longitudinal study of “non-institutionalized men of Japanese ancestry, born 1900-1919, resident on the island of Oahu” – began in October 1965. In all, 8,006 participants were studied and followed for the rest of their lives (Click here for more on this). 128 of the 8006 individuals enrolled in the study went on to develop Parkinson’s disease, and when the researchers went back and looked at the detail of their lives, they noticed something interesting about milk.
Title: Consumption of milk and calcium in midlife and the future risk of Parkinson disease
Authors: Park M, Ross GW, Petrovitch H, White LR, Masaki KH, Nelson JS, Tanner CM, Curb JD, Blanchette PL, Abbott RD.
Journal: Neurology. 2005 Mar 22;64(6):1047-51.
The researcher found that the incidence of Parkinson’s disease increased with milk intake. In fact, it jumped from 6.9/10,000 person-years in men who consumed no milk to 14.9/10,000 person-years in men who consumed >16 oz/day (approx. 1/2 a litre; p = 0.017). This result suggested that drinking a large cup of milk per day doubled your chances of developing Parkinson’s disease. The researchers noted that this effect was independent of calcium intake. Calcium (from both dairy and nondairy sources) inferred no increase/decrease in the risk of developing Parkinson’s disease. The effect was specific to milk.
Has anyone replicated this finding?
Unfortunately, yes. Two independent groups have found similar results:
Title: Consumption of dairy products and risk of Parkinson’s disease.
Authors: Chen H, O’Reilly E, McCullough ML, Rodriguez C, Schwarzschild MA, Calle EE, Thun MJ, Ascherio A.
Journal: Am J Epidemiol. 2007 May 1;165(9):998-1006.
PMID: 17272289 (This article is OPEN ACCESS if you would like to read it)
These researchers looked at the subjects (57,689 men and 73,175 women) enrolled in the American Cancer Society’s Cancer Prevention Study II Nutrition Cohort, and found a total of 250 men and 138 women with Parkinson’s disease. Dairy product consumption was positively associated with risk of Parkinson’s disease, 1.8 times that of normal in men and 1.3 times in women. When the dairy products were divided into milk, cheese, yogurt and ice cream, only milk remained significantly associated with an increased risk of developing Parkinson’s disease.
Title: Dietary and lifestyle variables in relation to incidence of Parkinson’s disease in Greece.
Authors: Kyrozis A, Ghika A, Stathopoulos P, Vassilopoulos D, Trichopoulos D, Trichopoulou A.
Journal: Eur J Epidemiol. 2013 Jan;28(1):67-77.
In this third study, the researchers conducted a population-based prospective cohort study involving 26,173 participants in the EPIC-Greece cohort. After analysing their data the investigators also found a strong positive association between the consumption of milk and Parkinson’s disease. And like the previous study, there was no association with cheese or yoghurt. The effect was again specific to milk.
So what is there something in particular in milk causing this effect?
That is the assumption, but we are not clear on what it is exactly. There is some new evidence, however, hinting that certain contaminants.
And this brings us to the research report from earlier this year:
Title: Midlife milk consumption and substantia nigra neuron density at death
Authors: Abbott RD, Ross GW, Petrovitch H, Masaki KH, Launer LJ, Nelson JS, White LR, Tanner CM.
Journal: Neurology. 2016 Feb 9;86(6):512-9.
In this study, the researchers looked at the milk intake data for 449 men in the Honolulu Heart Study (which were collected from 1965 to 1968), and then conducted postmortem examinations of their brains (between 1992 to 2004). The researchers found that subjects who drank more than 2 cups of milk per day during their midlife years had approximately 40% fewer dopamine neurons (in certain areas of a region called the substantia nigra where the dopamine neurons live).
But here is the interesting twist in the story:
None of these 449 subjects were diagnosed with Parkinson’s disease
These were all neurologically normal/healthy individuals.
Plus this particular effect was only observed among the milk drinking, non-smokers. The milk drinking smokers did not have this cell loss (smoking is associated with a reduced risk of developing Parkinson’s disease – click here for more on this).
The researchers then took the study a step further. They noticed that the cell loss effect was also associated with the presence of heptachlor epoxide in the brain.
What is heptac..whatever?
Heptachlor is an organochlorine compound that was used as an insecticide. Pesticides and insecticides have long been associated with increased risk of Parkinson’s disease (click here to read that post).
In this study, of the 116 brains analysed, heptachlor epoxide was found in 90% of the non-smokers who drank the most milk, but only 63% of those subjects who drank no milk. This lead the researchers to speculate as to whether contamination of milk by heptachlor epoxide could have caused the cell loss. We should point out here that this particular part of the analysis is a wee bit flimsy. The sample size for the non-smoking, high milk consumption group was very small: only 12 individuals.
So what does it all mean?
It means I am now dairy free.
EDITORIAL NOTE HERE: While we do not expect this post to crash the world wide milk market, we did not want to frighten any readers out of their habit of drinking milk. It should be noted here that the daily intake of milk associated with increased risk of Parkinson’s disease is very high (>16 oz/day or 1/2 a litre/day). Having said that lowering ones dairy intake does have many benefits for ones health.
In addition, in our last post, we discussed the microbiome of the gut and how the bacteria there could be influencing Parkinson’s disease. It would be interesting to see whether follow-up studies of that particular study highlight any insecticide/pesticide interactions with the bacteria of the gut.
One last thing: The purpose of today’s post was not to scare people out of drinking milk, but merely to throw a curious observation out there for people to think about. It will be interesting to hear what people think about this, especially any observations based on their own experience.
The banner for today’s post was sourced from AndFarAway
In 1950, Dr Tavia Gordon noticed that while the overall mortality rates for men in the USA and Japan were very similar, the incidence of heart disease was significantly lower in Japan. This observation resulted in three longitudinal studies – one of which became known as the Honolulu Heart Study.
Dr Travis Gordon. Source: JSTOR
The original purpose of the study was to determine whether there was a difference in heart disease incidence between Japanese people living in Japan and individuals of Japanese ancestry living in Hawaii.
The subjects recruited for the study were “non-institutionalized men of Japanese ancestry, born 1900-1919, resident on the island of Oahu.” In all, 12,417 men were identified as meeting the criteria. Of those contacted, 1,269 questionnaires were ‘return to sender’, 2,962 men declined to participate in the study, and 180 died before the study commenced. That left 8,006 participants who would be studied and followed for the rest of their lives.
From October 1965 onwards, the participants were interviewed and given physical examinations every few years. The interview processed asked for:
- Family and personal history of illness
- Sociological history
- Smoking status
- Physical activity level
The physical examination was very thorough, looking at:
- ECG (Electrocardiography – electrical activity of the heart)
- Urine analysis
- Measurements of weight, height, skinfold thickness, etc.
- Blood pressure and serum cholesterol
As a result, the study built up a HUGE amount of epidemiological information regarding these 8,006 individuals.
So, what does this have to do with Parkinson’s disease????
Given the enormous number of individuals involved in the study and the length of time that they were followed, it was inevitable that a certain percentage of them would develop Parkinson’s disease as the study progressed. As a result, the Honolulu Heart Study represents one of the largest epidemiological study of Parkinson’s to date. In 1994, a group of research involved in the study, published some very interesting findings relating to Parkinson’s disease. That published article was:
Title: Epidemiologic observations on Parkinson’s disease: incidence and mortality in a prospective study of middle-aged men.
Authors: Morens DM, Davis JW, Grandinetti A, Ross GW, Popper JS, White LR.
Journal: Neurology, 1996 Apr;46(4):1044-50.
In total, 92 of the 8006 individuals enrolled in the study developed Parkinson’s disease. The incidence of Parkinson’s cases was registered between 1965 and November 30th 1994. The majority of the cases were diagnosed between 55 and 79 years of age (n=80). Diagnosis after the age of 80 was very rare. It is interesting to note that when the researchers divided the group into those ‘born before 1910’ and those ‘born after 1910’, the older group (born before 1910) had a lower risk of Parkinson’s disease.
In another study, the same group of investigators noted
Title: Prospective study of cigarette smoking and the risk of developing idiopathic Parkinson’s disease.
Authors: Grandinetti A, Morens DM, Reed D, MacEachern D.
Journal: American Journal of Epidemiology 1994 Jun 15;139(12):1129-38.
In this study the authors found that men who had smoked cigarettes at any time prior to their enrollment in the study in 1965, had a reduced risk of developing idiopathic Parkinson’s disease (relative risk = 0.39). That is to say, smoking reduced the chance of developing Parkinson’s disease. And a few years later the authors published a follow up paper which rejected the possibility that smoking was killing people before they could develop Parkinson’s disease (selective mortality representing a false positive). That follow up report can be found here.
EDITOR’S NOTE: THIS DOES NOT MEAN THAT EVERYONE SHOULD RUSH OUT AND START SMOKING. THERE DOES, HOWEVER, APPEAR TO BE SOME INGREDIENT IN CIGARETTES THAT REDUCES THE INCIDENCE OF PARKINSON’S DISEASE. A LOT OF RESEARCH IS CURRENTLY TRYING TO IDENTIFY THAT INGREDIENT.
This finding was made alongside other interesting correlations (Note: coffee and alcohol reduce the risk of Parkinson’s disease):
From Grandinetti et al (1994).
It should be noted that many of these associations (smoking in particular) had been reported before, but the Honolulu Heart Study was the first epidemiological study providing definitive proof. And it should be noted that subsequent epidemiological studies have found similar results.
INTERESTING FACTS ABOUT THE JAPANESE:
- The Japanese as a population have a lower incidence of Parkinson’s disease (much like most of the Asian nations) than their western equivalents, despite living longer.
- Japan is the only country in the world where females have a higher incidence of Parkinson’s disease than men (and we have no idea why!). Look here for more on this.