It’s well known that both calcium and vitamin D are important for maintaining bone density as we age. However, research on the role of calcification in heart disease and a recent study showing that high doses of vitamin D failed to boost calcium absorption and bone mineral density raise questions about recommended intakes of these nutrients.
So what about the role of calcium in coronary artery disease (CAD)? The National Osteoporosis Foundation webinar this week summarized the research on this topic. The bottom line is that calcium intake is not related to artery calcification, but rather that calcium gets deposited in the coronary arteries in response to injury, sort of like a scar that forms to cover a wound. (More about this in another blog).
So for healthy bones and general health, the recommended adult calcium intake is 1,000 mg/day for adults 19-50 years and 1,200 mg/day for adults over 50 years. It’s always preferable to get as much calcium as possible from food sources, so estimate your dietary food intake, and then supplement as needed. The Nutrition Facts Label lists calcium as a percentage of the Daily Value (DV). For example, since the DV for calcium is 1,000 mg, 20% of the DV would be 200 mg/serving. If you find that your dietary intake of calcium is low, add supplemental calcium up to (but not exceeding) the recommended intake. Absorption of calcium from supplements is generally better when taken with meals at doses of 500 mg or less at a time.
Because calcium, magnesium and vitamin D work together in the body, it’s helpful to choose a calcium supplement that contains all three nutrients, and potentially vitamin K as well. Since vitamin D is needed by the body for calcium absorption and utilization, a balanced calcium supplement should contain about 150-200 IU vitamin D for every 300 mg calcium. And because magnesium intakes are often low, it’s a good idea to look for a calcium supplement that also contains at least a third as much magnesium as calcium per tab or capsule. See the Resource Section at the back of our book “Food for Thought” for a listing of the calcium and magnesium content of foods.
Obtaining adequate vitamin K is also important both for cardiovascular and skeletal health. There are two main forms of vitamin K. Phylloquinone (K1) is present primarily in green leafy vegetables and is the main dietary form of vitamin K. Menaquinones (K2), which are predominantly of bacterial origin, are present in modest amounts in various animal-based and fermented foods (like natto and kimchi), and are also produced by bacteria in the human gut. The recommended adult intake is 90 mcg/day for females and 120 mcg/day for males. A cup/day of dark green leafy vegetables would supply this amount or more.
While there is general consensus on the recommended daily intake of calcium, there is ongoing discussion about the amount of vitamin D recommended to maintain optimum blood levels for maximum health. The current recommended vitamin D intake for adults is: 200 IU/day for those aged 19-50 years; 400 IU/day for those 51-70 years; and 600 IU/day for those 71 years of age and older. The American Geriatrics Society and the National Osteoporosis Foundation recommend a slightly higher dose of vitamin D (800-1,000 IU/day) to reduce the risk of fractures and falls. While intakes up to 2,000 IU/day appear safe, toxicity is associated with intake of 4,000 IU/day or higher.
Based on its review of data of vitamin D needs, a committee of the Institute of Medicine (IOM concluded that practically all people are sufficient at levels ≥50 nmol/L (≥20 ng/mL). Despite the current scientific consensus about recommended vitamin D intake and blood levels, advocacy organizations like Grassroots Health recommend that vitamin D levels be maintained at 40-60 ng/mL for optimum health. According to charts available on their website, this could necessitate daily vitamin D intakes considerably higher than the intake amounts currently recommended, especially for those with blood levels lower than 50 ng/mL.
The health benefits of maintaining vitamin D blood levels above 20 ng/mL for bone health was recently questioned with the publication of a clinical trial published online on August 3, 2015. In this clinical trial, postmenopausal women without osteoporosis but with serum vitamin D averaging 21 ng/mL were randomly assigned to receive either 800 IU/day or 50,000 IU/month supplemental vitamin D or placebo. After one year of treatment, blood levels of vitamin D averaged 19 ng/mL in the placebo group, 28 ng/mL in the 800 IU/day group, and 56 ng/mL in the 50,000 IU/month group. Despite these changes in vitamin D blood levels, there were no differences in bone density, muscle function, muscle mass, or fall rate between the groups. Therefore, this study does not support vitamin D supplementation at levels required to raise blood levels above 20 ng/mL, at least for skeletal health.
So, to summarize calcium is important for skeletal health and does not cause vascular calcification (a risk for heart disease). If you find that your dietary intake is low, add supplemental calcium up to (but not exceeding) the recommended intake. And because calcium, magnesium and vitamin D work together in the body, it’s helpful to choose a calcium supplement that contains all three nutrients, and potentially vitamin K as well (if dietary intake is not adequate).
And speaking of calcium, enjoy Tofu for Beginners from our Food for Thought—Healing Foods to Savor. Tofu skeptics will be pleasantly surprised by this flavorful dish, which makes a nourishing appetizer or light meal. If you use tofu made with calcium salts (rather than with magnesium salts like nigari), a serving will provide 240 mg of calcium. Consider adding it to a tossed vegetable salad featuring baby greens to make a light meal rich in calcium, magnesium, and vitamin K. You can offer it as a scallop substitute in “Scallop Salad with Edamame and Sugar Snap Peas”.