Bone up on Calcium, Vitamin D Interactions

Featured Image Calcium And Vitamin D

As the age of our clientele creeps up, so do questions about safeguarding skeletal health. While obtaining crucial vitamins and minerals from whole foods benefits the body optimally, calcium and vitamin D supplementation continue to generate controversy. Expert’s, as well as layman’s, beliefs fall on a spectrum, from extolling the virtues of supplements as “the elixir of life” to stating modest, if any, benefits or harm, all the way to characterizing supplements as stepping stones to heart disease and death.

The Tandem Effect of Calcium/Vitamin D

Vitamin D, traditionally known as the “bone vitamin”, is vital to maintain bone mineral density. However, a tremendous amount of scientific data exists linking low concentrations of serum vitamin D to an increased incidence of cardiovascular disease and mortality, among other things like dampened immunity and cancer. Despite this alarming fact, most clinical trials have failed to find a positive link between vitamin D supplements and cardiovascular disease.

Several vitamin D–dependent calcium transport proteins regulate intestinal calcium absorption. Once absorbed into the small intestine, calcium and phosphorus can begin to form hydroxyapatite crystals which serve to strengthen/mineralize bones. Such knowledge substantiates the need for a diet rich in vitamin D as well as calcium for proper bone mineralization.

Sadly, the current US population tends towards insufficient levels of vitamin D. According to the Third National Health and Nutrition Examination Survey, 61% of white and 91% of black Americans suffer from severe vitamin D deficiency. As one can imagine, such insufficiency can certainly lead to calcium malabsorption and further deficiencies. Without adequate vitamin D, the body can absorb no more than 10% to 15% of dietary calcium. Even intestinal calcium absorption only approaches 30% to 40%.


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Another Risk for Older Adults

Older Americans especially seem to fall victim to vitamin D deficiency. It tends to go hand-in-hand with osteoporosis, one of the country’s biggest threats to our aging population. Several randomized trials recruiting physically challenged and ambulatory elderly subjects revealed how vitamin D in the absence OR presence of calcium reduced the rate of hip and/or nonvertebral fractures by 20-30%. The combination of vitamin D and calcium does seem to contribute to further reduction of fracture incidence.

Too Much of a Good Thing?

Whether suffering from osteoporosis or not, most adults remain unaware of the potential side effects of inappropriately high levels of calcium intake. Although rare in occurrence, overconsumption of calcium supplements can lead to a buildup that approaches toxic levels within the bloodstream. Some recent studies point to excessive calcium intake as increasing the risks of cardiovascular disease.

Some of the warning signs of excess calcium in the body include:

  • nausea, vomiting, constipation;
  • increased thirst or urination;
  • muscle/bone pain;
  • irregular heartbeat;
  • dry mouth/metallic taste in mouth;
  • confusion, fatigue, overall lack of energy.

Similar to calcium, ingesting high doses of vitamin D over the course of time may lead to dangerously excessive buildup since it is a fat-soluble nutrient and will accumulate in tissue. “Intoxication” occurs when blood levels reach 150 ng/ml (375 nmol/l) and really takes a high intake of D over an extended period of time. Since this fat-soluble vitamin remains stored within adipose tissue, getting gradually released into the bloodstream, the effects of toxicity may last for several months after ceasing supplementation.

Overdosing vitamin D may also result in excessive absorption of calcium, which in turn may lead to the potentially dangerous symptoms listed above. Please seek provider guidance when supplementing with vitamin D for more than a few months.

Form and Function of Vitamin D

Important biological differences exist between vitamins D2 and D3. Vitamin D3, considered the “active form” of the vitamin, offers a more profound effect on blood levels, significantly more than the synthetic form, vitamin D2. For those individuals keen on supplementation, opting for D3 saves your body the extra step of converting D2, hence its increased efficacy in terms of elevating blood vitamin D levels. Bear in mind that it takes approximately four times the amount of supplemental D2 than D3 to raise serum levels, both forms are better absorbed when in emulsified forms.


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Vexing Issue for Vegans

Most food sources of vitamin D hail from animals. Even the majority of vitamin D used in the preparation of supplements comes from lanolin (the wax secreted specifically from the sebaceous glands of wool-bearing animals). One primary challenge for many clients who have adopted a vegan lifestyle includes seeking out sources of calcium sufficient to meet their US RDA needs.

Vegans have the same calcium requirements as omnivores: 1,000 mg/day between the ages of 19 and 50; 1200 mg/day after age 50.  Therefore, in the absence of dairy products, how can vegans ensure their consumption of the proper plant-based foods in the appropriate quantities?

Many lentil-type protein sources, often overlooked, score highly in terms of calcium content. A mere ½ cup of great Northern beans, black beans, or navy beans dishes out 50 mg. of calcium. A half cup of calcium-fortified tofu, a favorite among meat-free consumers, offers a versatile and delicious way of obtaining 200 mg. of calcium per serving.

Mushrooms claim the title of the sole vegan food source that naturally contains a good amount of vitamin D. However, many vegan-safe foods receive vitamin D fortification during processing, including:

  • plant-based milk (flax, soy, or almond)
  • cereal
  • orange juice

Optimal absorption of fat-soluble vitamins such as vitamin D comes from pairing intake with a source of healthy nutritional fat, such as olive oil, avocado, nuts, or seeds.

Beware of the Offending Oxalates

Compounds known as oxalates, heavily present in some leafy green vegetables, can inhibit the absorption of calcium. Beet greens, Swiss chard, rhubarb, and spinach contain abundant quantities of calcium as well as other beneficial nutrients, but unfortunately possess high amounts of oxalates. However, by choosing alternative dark leafy greens — such as collard, kale, and mustard greens — which contain fewer oxalates, the calcium present in these vegetables gets absorbed at a very good rate.

Supplement Take-Home Message

At this time, experts advise against recklessly prescribing vitamin D supplements in an attempt to prevent cardiovascular disease, especially in conjunction with calcium supplementation. As with so many other examples, it seems in our best interests to strive for the recommended daily allowances of calcium intake through food, reserving supplementation for those at risk for severe deficiencies. In future studies, scientists will strive to more deeply examine the health effects of supplementation, prior to offering any solid recommendations for individuals of different genders, ages, and ethnicities.



Cathleen Kronemer is an NFPT CEC writer and a member of the NFPT Certification Council Board. Cathleen is an AFAA-Certified Group Exercise Instructor, NSCA-Certified Personal Trainer, ACE-Certified Health Coach, former competitive bodybuilder and freelance writer. She is employed at the Jewish Community Center in St. Louis, MO. Cathleen has been involved in the fitness industry for over three decades. Feel free to contact her at [email protected] She welcomes your feedback and your comments!