Technically known as phytonadione, vitamin K is a fat-soluble vitamin manufactured in the liver. According to Dr. Craig Feied, MD, director of the American Vein Institute and Associate Clinical Professor of Emergency Medicine at George Washington University, vitamin K is associated with veins and blood because it is a factor in the blood's ability to clot. Blood clots can choke off the blood flow through a vein or capillary and make it disappear. However, applying vitamin K to the surface of the skin won't make spider veins disappear, or even fade significantly. If vitamin K could penetrate the skin to affect the blood flow in spider veins, it could also affect the blood flow in healthy veins. If you're considering a vitamin K product for topical treatment of veins, this is not cause for alarm. In order for vitamin K to form blood clots you need to take large doses that are metabolized in the liver, where proteins are formed. These special proteins are what cause the blood to clot, and aren't related to topical application of vitamin K. Be aware that sunburns, heat, pressure on the face, injury, smoking, or repeated irritation or inflammation from irritating skin-care ingredients can increase the occurrence of spider veins. Avoid these and you can reduce the appearance of these veins, as well as their formation.
Vitamin K’s relation to the circulatory system has been parlayed into its use as a cosmetic ingredient to help diminish vascular conditions that emerge as skin imperfections such as dark circles under the eyes, redness from rosacea, and broken capillaries.
It is important to note that vitamin K in skin-care products is considered a cosmetic ingredient, not a pharmaceutical or drug. Therefore, cosmetics companies are not required to prove their claims about what they say it can do for skin. A typical claim for vitamin K, when applied topically, is that it can improve the appearance of dark circles under the eyes. A study published in the Journal of Cosmetic Dermatology (April 2004, page 73) examined the effect of applying a gel containing 2% vitamin K plus 0.1% retinol, vitamin E, and vitamin C. Fifty-seven adults with dark circles participated in this 8-week study and the results, while not a slam-dunk, weren't exactly discouraging either: 47% of the testers noted "fair to moderate" improvement in their dark circles. The majority of testers noticed no change, but the treatment was well-tolerated. As encouraging as this seems whether or not the results were from the vitamin K or the other vitamins is unknown. It also doesn't explain if the results were due to the impact of the antioxidants on skin or vitamin K' s effect on circulation when taken orally.
A smaller-scale study showed that topical application of a cream with at least 1% vitamin K (other strengths were used too) shortened the amount of time that skin is reddish-purple after a pulsed dye laser treatment. This indicated that when used in appropriate amounts, vitamin K exerts an anti-inflammatory effect on skin (Source: Dermatologic Surgery, December 1999, page 942). Again, it would have been more intriguing if this study examined other topical agents as a means to reduce post-laser discoloration. Since the study only included vitamin K, we don't know if a topical vitamin C product would have had similar benefits, not to mention green tea, alpha lipoic acid, superoxide dismutase, licorice extract, or curcumin (all well-documented topical anti-inflammatory agents). Almost no cosmetic companies are selling products with vitamin K near the amounts used in these studies. If you’re curious to try a topical product with more than a dusting of vitamin K, consider Donell Super Skin K-Derm Cream ($55 for 2.5 ounces; a gel version is also available but appears to contain less vitamin K than the Cream). Keep in mind that the studies did not look at vitamin K alone, but if you were curious if a good amount of vitamin K could make a difference, this product at least includes enough to prove that conjecture decidedly for yourself.