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Calcium, fertility and beyond

Updated: Jan 4

Several studies have shown that calcium is necessary for a healthy reproductive system, conception, and birth. In addition, once pregnant, the developing babies depend on the calcium they receive from their mothers. To improve fertility and to avoid risking bone loss during pregnancy, the OB/GYN community is in agreement that all pregnant women and those trying to conceive should increase calcium consumption. However, not all of them agree on the source of calcium. Some of them will suggest taking a prenatal with enough calcium, others will suggest consuming dairy products and others a rich whole foods plant-based diet. Let’s take a look at these options and see what recent studies have to offer us.


The American Pregnancy Association recommends that pregnant and lactating women take 1000 mg of calcium per day. Since the body cannot absorb so much calcium at once, it is not recommended to take 1000mg of calcium in a pill form. Dr. Erin Michos, MD, associate director of preventive cardiology for the Ciccarone Center for the Prevention of Heart Disease, said in 2016: “The body can’t process more than 500 milligrams of calcium at a time. If you take a supplement with more than that, your body has to do something with the excess. It’s possible that higher calcium levels in the blood could trigger blood clots or that calcium could be deposited along artery walls, which would contribute to the narrowing of blood vessels.”


In addition, taking calcium supplements by itself can disturb the delicate balance between other minerals, making it difficult for the body to absorb other key minerals such as zinc and iron. If the decision to take calcium supplements is made, taking a prenatal that takes into consideration the ratios between calcium, zinc and iron would be less damaging that just taking calcium by itself.


An article released by Johns Hopkins titled “Calcium Supplements: Should You Take Them?” highlights several studies where calcium supplementation was linked with an increased risk of colon polyps, kidney stones, and calcium buildup in the arteries of the heart contributing to heart attacks. A study published in 2016 titled “Calcium Supplements May Damage the Heart” analyzed 10 years of medical tests on more than 2,700 people in a federally funded heart disease study. The study conclude that taking calcium in the form of supplements may raise the risk of plaque buildup in arteries and heart damage. The study also highlights that a diet high in calcium-rich foods appears be protective.

Our study adds to the body of evidence that excess calcium in the form of supplements may harm the heart and vascular system.

Dairy Products

Milk, regardless of which animal it comes from, contains two classes of  proteins; whey and casein. Casein becomes clots or curds in the stomach, while whey remains liquid and is easier to digest. The heavy structure of casein allows for this protein to remain in the stomachs of un-weened mammals much longer – allowing them to absorb more nutrients. In human breast milk the ratio between whey and casein is about 80:20. In cow’s milk this ratio is the opposite –whey proteins representing only 18% of milk protein.

Pepsin, one of the most important digestive enzyme in humans, helps to break down proteins into smaller peptides and amino acids so that they can be easily absorbed in the small intestine. In order to break down casein, pepsin depends on another enzyme, rennin. Unfortunately, grown up humans don’t have this enzyme. Only a very small amount of rennin can be found in infant humans, but is totally absent in adults. On the other hand, rennin is found in large amounts in cows. In fact, it is the main source of milk digestion enzyme found in the fourth stomach of young ruminant animals.


There’s plenty of evidence showing that human adults do not benefit from drinking milk from cows or any other animal. In addition, there is extensive evidence showing that breast milk contains a variety of bioactive agents that modify the function of the gastrointestinal tract and the immune system, as well as brain development. Recent studies suggest that breast milk mitigates infant programming of late metabolic diseases - protecting them against obesity and type 2 diabetes. The World Health Organization recommends that infants should be exclusively breastfed for the first six month of life, and The American Academy of Pediatrics also recommends breastfeeding for at least 12 months.


The Abstract of a paper published by Methods, a peer-reviewed scientific journal, titled “Cow’s milk allergy: From allergens to new forms of diagnosis, therapy and prevention”, starts by saying “The first adverse reactions to cow’s milk were already described 2000 years ago. However, it was only 50 years ago that several groups started with the analysis of cow’s milk allergens”. Other sources suggest that the first adverse reactions to cow’s milk (skin and gastrointestinal symptoms ) were described by Hippocrates (prior to 370 B.C.).


According to Methods, cow’s milk is one of the first foods introduced into an infant’s diet and one of the most common causes of food allergy. Usually symptoms appear very early in life, after breastfeeding has stopped and cow’s milk is introduced into the diet. It is interesting to note that humans are the only mammals who consume the milk of other species, and into adulthood.


In addition, contrary to common belief, milk does not make bones stronger. A meta-analysis conducted by Critical Reviews in Food Science and Nutrition and published in 2020 concluded their systematic review by saying:

“We concluded that a greater intake of milk and dairy products was not associated with a lower risk of osteoporosis and hip fracture”

A study done in Sweden in 2014 titled: “Milk intake and risk of mortality and fractures in women and men: cohort studies”, concluded that:

“High milk intake was associated with higher mortality in one cohort of women and in another cohort of men, and with higher fracture incidence in women”


Meeting the calcium needs, pregnant or not, is a lot safer through diet. While the American Pregnancy Association recommends dairy products as a natural source of calcium, they also list collard greens, broccoli, watercress, kale, green soybeans, bok choy, rhubarb, figs (dried), oranges, white beans, chickpeas, and red beans. “When you get calcium through your diet, you’re taking it in small amounts spread throughout the day along with other food sources, which helps you absorb the nutrient” explained Dr. Michos.

The amount of nutrient absorbed and utilized by the body is known as bioavailability. For example, dairy foods have a bioavailability of about 30% absorption. This means that if the label on a carton of milk lists 300 mg of calcium per cup, about 100 mg will be absorbed and used by the body. On the other hand, plant foods like leafy greens contain less calcium overall but have a higher bioavailability than dairy. For example, bok choy contains about 160 mg of calcium per 1 cup cooked, but has a bioavailability of 50% - about 80 mg is absorbed. It’s interesting to note that eating 1 cup of cooked bok choy has almost as much bioavailable calcium as 1 cup of milk, and as mentioned earlier, 80% of the protein found in cow’s milk (casein) is undigestible by humans.

“When you get calcium through your diet, you’re taking it in small amounts spread throughout the day along with other food sources, which helps you absorb the nutrient"

Calcium and Fertility

According to a study by Nutrition Research, nutritional deficiency of some traces elements is a significant factor that affects semen quality and plays important roles in the male reproductive process. Human semen contains several trace elements (calcium, copper, manganese, magnesium, zinc, and selenium) that are necessary for normal spermatogenesis, sperm maturation, and motility. The influences of calcium deficiency on sperm function and male infertility have been widely studied. Calcium is involved in creating healthy sperm, maximizing sperm motility and helping with the fertilization of the egg. A  study published in 2019 by the International Journal of Fertility & Sterility concluded that:

“Calcium deficiency can be associated with reduced fertilization rate and male infertility. These data indicate that infertile patients may benefit from calcium supplementation."


Besides the most understood benefits of calcium, such as keeping our teeth and bones healthy, calcium also plays a crucial role in blood clotting, helping muscles to contract, and regulating normal heart rhythms and nerve functions. In addition, there’s plenty of evidence supporting the importance of calcium in creating healthy sperm, maximizing sperm motility and helping with the fertilization of the egg.  However, understanding how the different sources of calcium may affect one’s body is just as important as understanding its benefits.

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