Bone-Health Cofactors: New Science on Vitamin D, K2, Magnesium, and Zinc

Photo © iStockphoto.com/Devrimb

Loss of bone density impacts 54 million Americans, putting them directly in the path of danger of developing osteoporosis. Osteoporosis significantly increases risk of fracture, with studies suggesting that one in two women and one in four men over the age of 50 will experience a broken bone as a result. Estimates suggest that by 2025, osteoporosis will be the source of three million fractures and over $25 billion in healthcare costs each year.¹

Combating osteoporosis is a lifelong endeavor requiring prudent lifestyle choices. This includes exercise and also diet, with evidence indicating that nutrition plays a major role in promoting skeletal health.² Consuming the necessary vitamins and minerals from food as well as from dietary supplements should be an important pillar of any bone-health program. Take calcium. Calcium is well-known for its benefits to bone mineral density, as it is the most abundant mineral in the human body.³

Calcium’s effects, however, depend heavily on the actions of several other vitamins and minerals, including vitamin D, magnesium, vitamin K2, and zinc. We call these cofactors,
and they are believed not only to be critical to bone health but also to be most effective when present together in adequate amounts.

Vitamin D

Vitamin D is a crucial cofactor for bone health, as it regulates calcium balance and directly affects the osteoblast cells responsible for bone building and bone remodeling. Several studies link vitamin D deficiency with a higher risk of falls and fractures.⁴

Today, vitamin D deficiency is increasingly recognized as a worldwide epidemic, illustrated by the fact that more than 60% of postmenopausal women have inadequate serum levels of 25(OH)D, a common marker used to assess vitamin D status. The Institute of Medicine (IOM) defines vitamin D deficiency as serum levels of 25(OH)D less than 50 nmol/l (or 30 ng/ml). Vitamin D deficiency is a significant public health concern, and even populations of countries with abundant sun exposure often don’t meet target levels.⁵

But some newer clinical studies assessing vitamin D supplementation are yielding conflicting results. Ahead, we take a look at several.

For a Cochrane Database review, Alison Avenell and colleagues looked at interventional studies using vitamin D, or vitamin D in combination with calcium, and assessed the benefits of these nutrients for preventing hip fractures.⁶ Their review included 53 studies consisting of 91,971 participants categorized as postmenopausal women or older men.

Based on the research reviewed, the authors concluded that there is a lack of high-quality evidence that vitamin D intervention alone will prevent hip fractures in this population; however, they said, there is high-quality evidence that vitamin D in combination with calcium results in a small reduction in hip fracture risk. Also, they noted strong evidence linking the combination of vitamin D and calcium supplementation with a statistically significant reduction in the risk of new non-vertebral fractures.

The studies reviewed used a broad range of vitamin D doses, which may have impacted results. The authors emphasized that, while vitamin D is important for bone health, it was clear that the combination of vitamin D and calcium supplements was more effective than vitamin D alone for preventing fractures.

Kirsti Uusi-Rasi and colleagues in Finland aimed to determine the effect of exercise training, vitamin D, and the combination of both on reducing the risk of falls in older women.⁷ This two-year randomized trial included 409 white European women between the ages of 70 and 80 with a history of at least one fall during the previous year and no vitamin D use. The women were randomized into four groups: placebo, vitamin D (800 IU/day) without exercise, placebo plus exercise, and vitamin D (800 IU/day) plus exercise. The exercise routine comprised strength and balance training. The primary outcome was the number of monthly reported falls. The study also assessed bone density and measures of physical functioning, including muscle strength, balance, and mobility.

According to the researchers, vitamin D was not found to enhance the effect of exercise on physical functioning; however, vitamin D maintained femoral neck bone density measurements and increased trabecular density in the tibia.

Erin LeBlanc and Roger Chou are two of the contributing authors responsible for conducting a review on vitamin D for the U.S. Preventive Services Task Force.⁸ This task force determined that intervention with vitamin D was associated with an overall 11% decreased risk for falls. In an invited commentary accompanying the Uusi-Rasi study,⁹ LeBlanc and Chou state that adding the data from this well-conducted trial to the data they reviewed earlier does not change their conclusion supporting the potential benefits of vitamin D. They caution generalizing the results from this new study because the current study doesn’t represent the diversity seen in the U.S. population, they say. They also suggest that the dose of vitamin D (800 IU/day) may have been too low to enact change, considering that experts generally recommend daily doses between 1000 IU–2000 IU, especially in individuals at increased risk of falls. LeBlanc and Chou conclude that because of the low cost and low safety risk of vitamin D–based intervention, vitamin D should be kept in the armamentarium for prevention of falls.

In a Korean study, Hyeonmok Kim and colleagues from the Asan Medical Center at the University Of Ulsan College Of Medicine in Seoul conducted a study on 1,209 men and women aged 50 years and older to determine the association of vitamin D and femoral neck strength.¹⁰ The researchers analyzed bone mineral density measurements along with measures of femoral neck strength (including compression strength, bending strength, and impact strength) and found that both were significantly higher with increasing levels of vitamin D, and that these benefits were especially pronounced in women.

Additional clinical research provides important insights into the effects of vitamin D beyond direct effects on bone tissue. In a study evaluating the effects of vitamin D on bone mineral density and fracture risk, Jane Cauley, from the University of Pittsburgh, and colleagues enrolled 2,067 women with an average age of 48.5 years and who were entering menopause.¹¹ In the study, women from multiple ethnic groups were followed for an average period of 9.5 years, with researchers measuring serum levels of vitamin D as 25(OH)D at the third annual clinical visit. Bone mineral density and fractures were determined at each annual visit. The average 25(OH)D level was 21.8 ng/ml, and 43% of the women had serum levels lower than 20 ng/ml.

Women with 25(OH)D levels greater than 20 ng/ml had a 45% reduced risk of non-traumatic fracture over the 9.5-year follow-up period compared to those with 25(OH)D levels less than 20 ng/ml.

However, researchers did not find an association between serum vitamin D levels and traumatic fracture in this cohort, leading the researchers to speculate that the protective effects of vitamin D on fractures may be mediated by mechanisms other than increased bone mineral density. The ancillary benefits of vitamin D, including improvements in muscle strength as well as physical performance, may be more important than vitamin D’s effects on bone mineral density, they said.

Many researchers continue to speculate that a potential reason for the inconsistent results among vitamin D bone-health trials is that the administered dose may be too low.

Max Brincat and colleagues made this argument in a recent paper, pointing out that in many population groups, standard supplemental amounts fail to adequately raise vitamin D levels into the target range.⁵ While the Institute of Medicine defines vitamin D deficiency as serum 25(OH)D levels less than 50 nmol/l (20 ng/ml), the authors suggest that the appropriate target level in elderly individuals may be higher (75 nmol/l, or 30 ng/ml), and that doses higher than 800 IU–1000 IU per day would be required to achieve these targets. One bit of good news: David Dudenkov and colleagues from the Mayo Clinic found no increased risk of toxicity with serum 25(OH)D levels over 50 ng/ml, affirming the safety of higher doses.¹²

Based on the research, vitamin D clearly supports healthy bone mineral density and benefits muscle strength and physical performance in aging individuals; however, vitamin D works best in combination with adequate calcium. Several other nutrients also contribute to calcium and vitamin D’s actions.

Magnesium

Magnesium makes up nearly 1% of bone mineral content. Magnesium is directly required for the transport of calcium ions across cell membranes. Inadequate magnesium intake has been shown to result in low blood levels of calcium as well as resistance to some of the actions of vitamin D.

“Magnesium is necessary to convert vitamin D into its active form so that it can ‘turn on’ calcium absorption,” says Todd Johnson, director of marketing at Albion Minerals (Clearfield, UT), a leading manufacturer of mineral chelates.

Decreased magnesium content causes bone to become more brittle. “Research has shown that magnesium deficiency is a frequently occurring disorder that can lead to loss of bone mass, abnormal bone growth, and skeletal weakness,” Johnson says.

Unfortunately, it’s become clear that people aren’t getting enough magnesium through diet alone. Worse still, magnesium deficiency is more common in the elderly,¹³ potentially placing the population at higher risk of osteoporosis and other bone-health defects.

Experiments conducted in mice bone marrow cells have found that magnesium deficiency results in increased formation of bone-resorbing osteoclast cells.¹⁴ But recent studies showed that in female rats with sufficient calcium intake, magnesium supplementation led to increased bone mineral density and bone size by improving bone tissue metabolism.¹⁵

Sara Castiglioni and colleagues from the University of Milan in Italy identified several mechanisms whereby deficient magnesium levels adversely impact bone.¹⁶ First, magnesium deficiency leads to an altered structure of apatite crystals in bone, decreasing stiffness as well as bone’s load-bearing capacity. Magnesium deficiency also decreases the activation of vitamin D. By contrast, correcting magnesium deficiency through supplementation has been shown to normalize vitamin D metabolism. Magnesium deficiency also leads to low-grade inflammation, which is detrimental to bone health. Magnesium may additionally act as an important buffering agent, thereby protecting against osteoporosis onset.

But that’s not all. Metabolic acidosis is common in aging adults consuming a western diet and has been shown to influence calcium loss from bone, inhibit the activity of osteoblasts, stimulate osteoclast activity, and negatively affect bone mineralization. By also buffering excess acidity, it is likely that magnesium further protects against the development of osteoporosis.

In an analysis of women participating in the Women’s Health Initiative Observational Study, Tonya Orchard and colleagues estimated total magnesium intake and compared this to overall bone mineral density.¹⁷ They found that postmenopausal women consuming greater than 422.5 mg of magnesium daily had higher hip and whole-body bone mineral density than women who consumed less than 206.5 mg of magnesium daily on average. (Interestingly, however, the incidence of hip and total fractures did not differ across different intakes of magnesium in this cohort. In fact, the risk of lower arm and wrist fractures increased with higher magnesium intakes. The authors posit that this may be because the women who had the highest magnesium intakes were more physically active and thus likelier to experience falls.)

Another recent study confirmed the benefits of magnesium to physical performance in postmenopausal women. Nicola Veronese and colleagues from the University of Padova in Padova, Italy, enrolled 139 healthy women with an average age of 71.5 years in a randomized controlled trial in which participants were allocated to a control group or were supplemented with 300 mg of magnesium daily for 12 weeks.¹⁸ Exercise and fitness ability were assessed at baseline and again after 12 weeks.

The group supplementing with magnesium showed significant improvements in physical performance compared to the control group, suggesting that magnesium supplementation is an important factor in delaying the onset of deterioration of physical performance associated with age.

Vitamin K2

Vitamin K-and more specifically vitamin K2, the menaquinone form of vitamin K-continues to shine as a vitamin that supports multiple aspects of bone health. Vitamin K2 plays a direct role in transporting calcium from circulation into bone tissue by activating (carboxylation) two key calcium transport proteins in the bloodstream: matrix Gla protein, which transports calcium from circulation into bone, and osteocalcin, which reduces calcification of arteries and plays a significant role in bone development.^19,20

Furthermore, vitamin K2 has been shown to work hand in hand with vitamin D in multiple ways. Vitamin D enhances the absorption of calcium from the intestinal tract into circulation, while vitamin K2 aids calcium’s transport into bone tissue. Additionally, vitamin D promotes the production of osteocalcin from the bone-building osteoblast cells, while K2 serves to activate osteocalcin to perform its calcium-transport function.¹⁹

Research continues to validate vitamin K2’s benefits to bone health and heart health. Two common supplemental forms of vitamin K2 are menaquinone-4 (MK-4) and menaquinone-7 (MK-7), with the number designations referring to the length of the molecular side chains.  

Z.-B. Huang’s group from Zhejiang, China, conducted a meta-analysis assessing the role of vitamin K2 in the prevention and treatment of osteoporosis in postmenopausal women.²¹ In reviewing 19 randomized controlled trials consisting of 6,759 participants, the authors found that in postmenopausal women with osteoporosis, vitamin K2 supplementation achieved significant improvement in vertebral bone mineral density and reduction in the overall risk of fractures. Vitamin K2 also led to a decrease in under-carboxylated (inactive) osteocalcin, thus favoring bone mineralization.

Earlier, Martinus Knapen and colleagues from the Netherlands conducted a three-year, placebo-controlled study in healthy postmenopausal women to assess the effects of vitamin K2 MK-7 on bone health.²² Participants supplemented with 180 mcg/day of MK-7 or a placebo.

MK-7 supplementation led to increased bone strength and a decrease in the rate of decline of bone mineral content and bone density that normally occurs as a result of the aging process. The researchers also found less loss of vertebral height in the mid-back compared to placebo treatment, suggesting that MK-7 is a nutritional factor impacting both bone density and strength in postmenopausal women.

Zinc

Zinc is essential to human health. It plays a critical role as a structural component of proteins, acts as an enzymatic cofactor, and functions as a transcriptional regulator for a large array of cellular and biochemical processes.

Studies in cultured osteoblasts have shown potent stimulation of bone formation following exposure to zinc, leading to enhanced deposits of calcium. Additional studies found that by inhibiting nuclear factor-kappa B, a potent mediator of inflammation and bone resorption, zinc was able to suppress the differentiation of osteoclasts, inhibiting bone resorption.²³

Sadly, zinc deficiency is also widespread in the global population-a fact that animal research has shown may impact the normal physiological action of vitamin D on calcium metabolism²⁴ and interfere with the anabolic activity of vitamin D on bone tissue.²⁵

Payal Bhardwaj and colleagues from Punjab University in Chandigarh, India, conducted a study in a rat model of postmenopausal osteopenia to investigate the impact of zinc supplementation on prevention of bone loss.²⁶ They found significant changes to the cortical bone structure in rats in which estrogen deficiency was induced, including poor microarchitecture and resorbed areas of bone tissue. Zinc supplementation was able to arrest these changes, while improving overall bone microarchitecture, enhancing antioxidant defenses in bone tissue, and improving regulation of several markers of bone metabolism.

Additionally, a meta-analysis by Jianmao Zheng and colleagues from Sun Yat-sen University in Guangzhou, China, looked at published human studies relating serum levels of several minerals to the incidence of osteoporosis and concluded that low serum levels of zinc seem to be an important risk factor for this disease condition.²⁵

Strong Evidence

Maintaining optimal bone health requires a lifelong habit involving sound dietary and lifestyle choices.

Adequate calcium intake through diet and supplementation is essential. However, it is just as essential to consume sufficient and balanced amounts of critical cofactors for healthy bones-either via food or supplement-including vitamin D, magnesium, vitamin K2, and zinc.

Together, these important nutrients work to ensure that the metabolic processes supporting bone remodeling work efficiently for a lifetime.

Also read:

Here's to Good Bone Health: Calcium Fortification for Beverages

New Stability Data on Unique Encapsulated Vitamin K2

Vitamin K2 for Bone, Heart Health: Just the Tip of the Research Iceberg?

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