Vitamin K: A Research Roundup?>

Vitamin K: A Research Roundup

by Wellness Letter  

Here's a look at some of the clinical trials, meta-analyses, and observational studies that have examined vitamin K's role in bone and heart health over the past 15 years.

Bone health: a sampling of clinical trials using supplements

A systematic review and meta-analysis of 13 clinical trials, published in the Archives of Internal Medicine back in 2006, found that very high doses of vitamin K2 (MK-4, usually 15 to 45 milligrams a day) or K1 (1 to 10 milligrams), taken for 6 to 36 months, helped maintain bone mineral density (BMD); K2 also reduced the risk of hip and other fractures by at least half. Most of the trials were done in Japan, involved postmenopausal women, and used vitamin K2; five studies involved women with osteoporosis.

In a Canadian study in PLOS Medicine in 2008, high-dose vitamin K1 (5 milligrams a day) taken for two years did not protect women with osteopenia from age-related decline in BMD. In a study from the University of Wisconsin, Madison, in the Journal of Bone and Mineral Research in 2010, healthy postmenopausal women who took either vitamin K1 (1,000 micrograms a day) or K2 (MK-4, 45 milligrams a day) for a year did no better in terms of BMD or markers of bone health than those taking a placebo.

In a Japanese study in the Journal of Bone and Mineral Research in 2010, people with osteoporosis who took vitamin K2 (MK-4, 45 milligrams a day) for two years maintained BMD and reduced the risk of fractures by more than half {65%}, compared to a placebo.

In a study in the Journal of Korean Medical Science in 2011, postmenopausal Korean women who took vitamin K2 (K-4, 45 milligrams a day) plus vitamin D and calcium for six months had increased BMD compared to those taking just D and calcium.

A Dutch clinical trial in Osteoporosis International in 2013 found that postmenopausal women who took vitamin K2 (MK-7, 180 mcg a day) for three years had reduced age-related decline in BMD and decreased loss in vertebral height in the lower spine compared to a placebo. Some other clinical trials since the 2006 review have found that neither vitamin K1 nor K2 supplementation had an effect on bone mineral density in older people.

A meta-analysis, published in Osteoporosis International in 2015, focused on 19 clinical trials (mostly from Japan) on vitamin K2 (usually MK-4) for the prevention and treatment of osteoporosis in postmenopausal women. It found that, compared to a placebo, the supplement improved vertebral BMD and bone biomarkers in women with osteoporosis; it did not improve lumbar or hip BMD in women without osteoporosis. In the seven trails that reported incidence of fracture, the vitamin did not reduce the risk.

Cardiovascular health: mostly observational research

Several Dutch observational studies have linked high dietary intake of vitamin K2 (but not K1) to cardiovascular benefits, independent of other dietary factors. In a study in the Journal of Nutrition in 2004, a high dietary intake of vitamin K2 was associated with reduced coronary calcification, coronary heart disease, and coronary mortality in healthy people over age 55 who were followed for seven years, compared to a low intake.

Similarly, a study in Nutrition, Metabolism & Cardiovascular Diseases in 2009 found that a high intake of vitamin K2 was associated with a reduced risk of coronary events in postmenopausal women. Another one in Atherosclerosis in 2009 linked high K2 intake by postmenopausal women with reduced coronary calcification. Still another Dutch study, in Atherosclerosis in 2016, found that high dietary intake of K2 was associated with a reduced risk of peripheral artery disease, especially in people with hypertension.

Few clinical trials have been conducted on the cardiovascular effects of vitamin K supplementation. A Tufts University study in the American Journal of Clinical Nutrition in 2009 looked at people (ages 60 to 80) with pre-existing coronary artery calcification. Those who consistently took 500 micrograms of vitamin K1 a day for three years had slower progression of calcification, compare to those taking a placebo. Such results are merely “hypothesis generating” and need to be confirmed by other studies, according to the researchers.