Consumption of dairy products is linked to many of the common diseases of aging. Discussion on the influence of dairy foods on chronic disease in this series began in Part 2, Part 3 and Part 6 but unfortunately it is not over yet. Dairy foods exert their effects on a wide range of diseases and conditions including cardiovascular disease, cancer, diabetes, auto-immune diseases, neurodegenerative diseases, disorders of sperm and rate of cognitive decline.
Consuming dairy products is linked to increased cardiovascular disease risk
Studies have observed higher rates of death from cardiovascular disease with increasing milk intake. For example, in women who drink three or more glasses of milk a day the risk of death from cardiovascular disease is almost twice as high as the risk associated with those drinking less than one glass of milk a day. In men, the overall risk of death increased about 10 % when they drank three or more glasses of milk daily (1).
Dairy products, including milk and especially cheese, are the largest source of saturated fat in the Western diet. The fat in milk and dairy products is about 66% saturated fat (2). Cheeses can contain 70% of total calories from fat (3). Milk products also contain cholesterol. Diets high in saturated fat and cholesterol are consistently linked to increased risk of heart disease (4,5,6,7,8,9,10,11).
Trans-fats are created when oils are partially hydrogenated in order to make them more solid at room temperature. However, trans-fats also exist naturally in animal-based foods. Whole milk and cheese contain about 2.5% trans-fats (12). Though this may seem like a small amount, the US National Academies of Science have concluded that the only safe intake of trans-fatty acids is zero, saying that any increases in intake of trans-fats, regardless of their source, increases risks of cardiovascular and coronary heart disease (13,14).
Consuming dairy products is associated with higher risk of auto-immune diseases such as multiple sclerosis and type-1 diabetes
The human immune system is continually monitoring our bodies for threats to our wellbeing, looking for unfamiliar molecules, cells and other elements. Sometimes the foreign substances it identifies are so similar to our own body components that the immune system will misidentify our own tissue as unknown and possibly dangerous and launch an attack against that tissue. This is known as molecular mimicry and is the prevailing hypothesis for the mechanism of auto-immune disease (15,16). Some of the proteins present in dairy foods are very similar to our own and, perhaps not surprisingly, dairy products are associated with several immune-related disorders.
One of these is Multiple Sclerosis (MS). In this condition the immune system attacks the protective sheath around neurons causing neurological problems. Consumption of cow’s milk appears to be a significant risk factor for developing MS with studies showing a highly significant correlation between milk consumption and prevalence of MS and a lower but still significant correlation between cream and butter consumption and prevalence of MS (17,18).
The association with cow’s milk protein with development of type-1 diabetes has been known for many years (35). In 2015 a study called DAISY (the Diabetes Autoimmunity Study in the Young) followed 1,835 children at increased risk of diabetes (siblings and offspring of diabetes patients and children with a genetic profile linked to increased development of diabetes) and found that both lactose and protein from cow’s milk were linked to pancreatic islet cell auto-immunity and subsequent progression into type-1 diabetes. High cow’s milk intake by these children was associated with a 41% increase in the risk of islet auto-immunity and a 59% increase in further progression into type-1 diabetes. The study results suggest that introduction of cow’s milk before six months of age may prime the immune system to produce cells that react specifically with insulin leading to both islet auto-immunity and type-1 diabetes development. One of the mechanisms underlying this reaction is thought to be the response of gut bacteria to cow’s milk protein (36).
Consuming dairy products is associated with the neurodegenerative diseases, Parkinson’s Disease and Huntingdon’s Disease
Parkinson’s Disease is a neurodegenerative disease that reduces the ability of nerves in the brain to communicate with each other. The condition results in difficulty in movement with symptoms such as tremor; slowness and stiffness; impaired balance; and rigidity of the muscles (19). There are clear-cut associations between the consumption of milk and the incidence of Parkinson’s, however it is difficult to pinpoint the component in milk that may be the cause. Prospective cohort studies which follow people over time have revealed that the risk of Parkinson’s Disease increases by 17% for every cup of milk consumed daily and 13% for every daily 10 gm slice of cheese eaten (20).
Huntingdon’s Disease is an inherited brain disorder that produces involuntary movements including diminished coordination; difficulty walking, talking and swallowing; impaired cognition; irritability; depression; and anxiety (21). Dairy consumption is linked to a doubling of the risk of early onset of Huntingdon’s Disease (22,23).
Neurotoxins in milk have been implicated in Parkinson’s Disease because the brains of its victims contain high levels of organochlorine pesticide residues and so does milk (24). Other research suggests that the sugars in milk such as lactose and galactose may be related to the development of these harmful neurological diseases (25). Further research will provide more insight into the mechanism but, whatever is at the root of this neurodegenerative damage, avoiding milk may be an effective step towards its prevention.
High saturated fat intake from dairy products is linked to reduced semen quality
A 2013 study showed that high dietary intake of saturated fat is linked to reduced semen quality along with lower sperm concentration and total sperm count in men. Men eating the most saturated fat had a 38% lower sperm concentration and a 41% lower total sperm count compared to men eating the least saturated fat (26). Since a significant percentage of saturated fat intake in the study participants came from dairy products, the effect on semen and sperm was suggested to be due to residues of industrial chemicals that accumulate up the food chain and become concentrated in the fat and milk of dairy cows. Some of these chemicals are recognized hormone disrupters. Milk fat is likely one of the highest dietary sources of exposure to these chemicals.
Cheese consumption is associated with reduced concentration of sperm in men who smoke currently or smoked in the past. In a 2014 investigation those participants eating the most cheese showed 53% lower sperm concentrations than men eating the least (27).
The hormones present in some animal foods are another potential cause for sperm damage. All foods derived from animals contain oestradiol, a natural sex hormone that is identical to the oestradiol found in humans (28). Estrogens are found in meat and eggs but are highest in dairy products (29,30). This is because modern dairy cows continue to produce milk throughout their pregnancies during which estrogen levels increase by as much as 30 times. Estrogen levels in dairy cows are mirrored in their milk (31).
Other studies also reveal that full fat dairy intake, particularly that of cheese, is associated with less mobile sperm, abnormal sperm shape and low total sperm count. Researchers have stated that, though estrogens from dairy could be causing these effects, study results suggest other processes may be involved. Two other mechanisms are proposed that might explain the results of these investigations;
1 – Dairy intake may be causing direct testicular damage leading to lower sperm mobility and abnormal sperm shape.
2 – Environmental contaminants in dairy such as pesticides and chlorinated pollutants may be causing lower sperm quality and interfering with hormonal feedback to cause decreased sperm production (32).
Consuming milk is associated with faster cognitive decline
A study from 2017 found an association between greater milk intake at midlife and greater rate of cognitive decline over a 20-year period (33). These results were consistent with those from earlier studies (34).
Intake of dairy products appears to contribute to a number of debilitating chronic conditions. Limiting or avoiding the intake of milk and other dairy products is one step that has the potential to decrease the risk of developing multiple diseases.
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