When I was diagnosed with hyperparathyroidism my primary care physician and endocrinologist suggested me to have lots of dairies in diet to get calcium, since the patients with hyperparathyroidism are at greater risks of osteoporosis or bone loss. Weakening bone is positively correlated with kidney stone, arterial calcification, aortic valve stenosis, and cardiovascular disease. It is ‘well accepted’ that milk and dairy is a rich source of calcium which protects bone; some dairy products like cheese also contains vitamin K2, which lowers the risk of cardiovascular disease. However, this ‘well accepted’ fact is challenged by a recent article published in a highly prestigious journal ‘The New England Journal of Medicine’ by Dr. David S. Ludwing.
Role of milk on bone health, cancers, and obesity:
Dairy from non-human mammals is a major part of western diet and some Asian countries as well. In US, the daily recommended intake of milk or equivalent portions of other dairy products (like cheese, or yogurt) is 24-oz or 3 servings per day for adults as well as children at age of 9 or older, which is based on the nutritional requirements of calcium.
Besides calcium, cow’s milk is a rich source of branched chain amino acids (made up of leucine, isoleucine, and valine) which raises the plasma concentration of insulin-like growth factor I (IGF-I). IGF-I is a growth hormone and as the name suggests, it causes everything to grow big. Leucine specifically triggers the mammalian target of rapamycin pathway (mTOR), which promotes cell growth and inhibits cell death. Cell death is a necessary physiological process to remove damaged cells from the body and promiscuous cell growth leads to cancer.
Cows these days are bred to have higher levels of IGF-I, which makes the breeds larger in size, and heavier in milk. And these cows are milked throughout their pregnancy, which vastly enhances the number and levels of hormones in the milk, including sex hormones like estrogens and progesterone.
Higher levels of IGF-I cause accelerated growth and tall adult stature, which is found to be linked with higher risk of hip fracture, pulmonary emboli, and cancers. Increased plasma IGF is an important predictor of prostate cancer. In prospective cohort studies, milk consumption is highly associated with the greater risk of prostate cancer, especially aggressive forms. Total dairy intake has also been linked with the endometrial cancers, particularly in post-menopausal women possibly attributed to the sex-hormone content of dairy products.
Milk is also high in phosphorous and tend to positively correlate with bone mineral density like calcium. The lower the milk fat the higher the phosphorous content. However, milk is not a great source of vitamin D. Without adequate vitamin D, calcium and phosphorous leaves the body through the kidneys in the urine. Hip fractures is highest in countries having highest intake of milk and calcium.
Like adults, dairy intake or calcium supplementation in children although increases bone mineral density in an insignificant amount, the increases do not persist after discontinuation, which suggests that high consumption of dairy or calcium throughout childhood cannot serve as a calcium ‘reservoir’ for their adult life and reduces fracture risk.
Further studies with adolescence or young children show, while full fat milk reduced the risk of obesity, consumption of low-fat milk was positively correlated with weight gain or higher BMI, which could be attributed to the higher energy intake. Thus, USDA recommendation to choose reduced or low-fat dairy over full fat does not appear to have any added benefits on wight control.
Milk, growth hormone, and longevity:
Study shows, the dwarf mice, which are a third the size of their normal counterparts due to the lack of growth hormone, lives typically a year longer than their normal-sized counterparts, which is in human equivalent of living 105 years, instead of 70 years [2]. Theses mice are also resistant to cancer or tumor growth, could be attributed to the free radical accumulation though the exact reason is yet to be revealed [2]. Contrarily, giant mice that are genetically modified to overproduce growth hormones age prematurely and live only 8 or 9 months [2].
Milk and Dairy on inflammation:
Dairy is in the list of top inflammatory foods. Dairy from grass-fed or organic cow’s is a better option. Grass-feeding increases their omega-3 content, however milking throughout the pregnancy is also widespread among organic milk producers, which vastly raises the sex-hormone contents of the milk. Milk also naturally contains lactose and Casein A protein. Lactose is a natural sugar that is digested in our small intestine by an enzyme called lactase. Nearly 70% of people around the world is lactose intolerant. Undigested lactose moves to the large intestine, where bacteria interact with the undigested lactose and causes abdominal pain, bloating, gas, diarrhea, and discomfort. The same symptoms may also arise from casein A1 protein in milk from cows breed mostly in Australia, Northern Europe, and United states [3].
Takeaway
Milk is a nutrient dense food which could be beneficial for the people if the overall calorie intake is low or if the diet quality is poor. If the calorie intake or diet quality is high, then having increased milk and dairy consumption as recommended by USDA, may actually poses health risks. For calcium alternatives, some dark leafy greens (such as kale, arugula, broccoli), as well as fish with bones (sardines) could be preferrable options.
References
1. Willett, W. C., & Ludwig, D. S. (2020). Milk and health. New England Journal of Medicine, 382(7), 644-654.
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