Bisphosphonates are the most commonly prescribed drugs for osteoporosis—the fragile-bone disease that affects some 200 million people worldwide.1 But while these drugs may be effective for reducing the risk of bone fractures, they can also have serious side-effects, including heart problems, stomach ulcers and osteonecrosis of the jaw, or ‘dead jaw’ syndrome.
The good news is that scientists have been busy investigating alternative treatments for osteoporosis, and one in particular—a vitamin found naturally in leafy greens and fermented foods—is showing a lot of promise.
Vitamin K: the secret bone booster
When Danish researcher Henrik Dam discovered a substance essential for blood clotting in the 1930s, he named his new find ‘vitamin K’, after the German word for ‘coagulation’. But the latest research shows that this fat-soluble nutrient plays an important role in bone health too.
There are two basic forms of the vitamin: vitamin K1, or philloquinone, found in in dark-green leafy vegetables like kale, spinach and cabbage; and vitamin K2, or menaquinone, found in meat, cheese and fermented products like natto (made from soybeans).
Several studies suggest that not getting enough vitamin K1 can increase the risk of fractures,2 while those who eat a lot of natto, high in vitamin K2, seem to have a lower risk of bone loss.3
So can vitamin K supplements be used to prevent and treat osteoporosis?
Vitamin K2 trials
The Japanese certainly think so, and have pioneered the use of vitamin K2—which appears to exert a more powerful influence on bone than does K1—as an osteoporosis treatment.4 In a two-year study of 241 women with osteoporosis enrolled at the Research Institute and Practice for Involutional Diseases in Nagano, Japan, a high oral dose (45 mg/day) of vitamin K2 (in the synthetic form known as menatetrenone) significantly reduced the rate of fractures compared with a placebo and prevented bone loss in the lower (lumbar) spine.5
In another Japanese trial, menatetrenone at the same dose was just as effective as the bisphosphonate drug etidronate at reducing spinal fractures in postmenopausal women with osteoporosis. It also significantly increased bone mineral density (BMD), although to a lesser extent than did the drug.6
As postmenopausal women are at particular risk for osteoporosis, much of the vitamin K research has focused on this group. In a recent review of eight randomized, controlled trials of postmenopausal osteoporosis, vitamin K2 therapy was shown to increase BMD in the lumbar spine, albeit modestly, and to reduce the incidence of any spine vertebral fractures.7
And in healthy postmenopausal women, studies have found that taking K2 can help prevent osteoporosis by improving bone metabolism and halting bone loss—even at low doses. In one three-year study, just 180 mcg/day of a natural form of K2 called menaquinone-7 (MK-7) reduced the age-related decline in spine and femoral BMD and improved bone strength.8
Vitamin K2 can also prevent the bone loss typically seen in patients with Parkinson’s disease,9 cirrhosis of the liver,10 stroke11 and anorexia.12
Safety and side-effects
Vitamin K2 supplements appear to be safe even at the high doses used in many of the studies. Nevertheless, because of its blood-coagulating properties, vitamin K should not be taken with blood-thinners like warfarin.
In general, though, K2’s safety profile makes it an attractive alternative to bisphosphonates, which have been linked to a litany of adverse effects, ranging from serious heart rhythm abnormalities to stomach ulcers and oesophageal damage.13
Ironically, the drugs can also cause bone problems like osteonecrosis of the jaw,14 where bone tissue fails to heal after even minor trauma such as tooth extraction. This can lead to bone infection and fracture, and may require long-term antibiotics and surgery to remove the dead bone.
Bisphosphonates can even increase the risk of fractures. In one study, women taking bisphosphonates regularly for more than five years had a reduced risk of ‘typical’ osteoporotic fractures, but they also had nearly three times the risk of ‘atypical’ fractures, such as breaks in the shaft of the femur (thigh bone), compared with women taking the
drugs only occasionally or for less than 100 days.15
The bottom line
There’s good evidence that vitamin K, specifically K2, can strengthen bones, prevent bone loss and reduce the rate of fractures in people with osteoporosis or at risk of developing the condition, making it a useful nutrient for both the prevention and treatment of fragile bones—especially considering the risks associated with bisphosphonate drugs. Although much of the research involved high doses of a synthetic form of K2, this was found to be safe and well tolerated, and lower doses of a natural form of K2 are showing promise for bone health too (see box, right).
Still, osteoporosis is best tackled through a multipronged approach—one that incorporates a range of bone-healthy nutrients as well as dietary and lifestyle changes. In fact, a combination of vitamin K2 and vitamin D3 has been found to be more effective at increasing BMD in osteoporosis sufferers than either nutrient on its own.16
For more information on beating osteoporosis, see WDDTY April 2014.
Which form of K2?
Vitamin K2 (menaquinone) comes in a variety of forms. Much of the early research into vitamin K and osteoporosis used a synthetic form of menaquinone-4 (MK-4) called ‘menatetrenone’, typically at a high dose of 45 mg/day. But more recently, the research has focused on menaquinone-7 (MK-7), a form found naturally in the Japanese fermented soy food natto, and readily available in a synthesized supplement form.
MK-7 appears to have a number of advantages over MK-4, the main one being its greater bioavailability and efficacy at lower dosages.1 For this reason, experts recommend taking supplements of this MK-7 form of K2 at doses of around 100–300 mcg/day.
You can also get a good dose of K2 by eating plenty of natto, although many may be put off by its smell and slimy texture, and it may also be hard to find except in Asian supermarkets.
On the other hand, vitamin K1 is also important for bone health, and is abundantly found in leafy green vegetables like kale, spinach and collards, so you can easily up your K1 intake by making sure to eat your greens.