Ask the Experts: Vitamin K; Shark Cartilage Supplements

Q: What is vitamin K and what role does it serve in the body?

A: Vitamin K is an umbrella term for a group of fat-soluble vitamins which play an essential role in coagulation, or blood clotting (“K” is from the Danish word “koagulation”). Vitamin K also improves bone health. Natural forms of vitamin K fall into two categories: phylloquinones (vitamin K1 from plants) and menaquinones (vitamin K2 from bacteria). Since the body has limited vitamin K storage capacity, regular adequate intake is important (90 micrograms/day for women and 120 micrograms/day for men). This is easy to achieve with about 1 cup/day of dark green leafy vegetables such as kale, spinach, Brussels sprouts, or broccoli. Deficiency is rare in healthy adults but can cause bleeding or bruising and increase osteoporosis risk. Those at high-risk for deficiency include people with chronic malnutrition, digestive diseases, and infants (who commonly receive a vitamin K injection at birth). While toxicity from dietary vitamin K is uncommon, patients taking blood thinners (warfarin) should keep intakes consistent as sudden fluctuations may alter drug effectiveness.

—Bridget Cassady, PhD, RDN

Q: How is shark cartilage used as a supplement?

A: Supplements derived from shark cartilage, the tough tissue that supports the animal’s skeleton, gained popularity in the 1980s when this compound was touted as a cancer cure, particularly for Kaposi sarcoma. It was also purported to help manage arthritis, psoriasis, and wound healing.

Effectiveness. Shark cartilage has remained a widely used supplement by persons with cancer. However, convincing scientific evidence to substantiate its use is lacking, acccording to the Natural Medicines Comprehensive Database.

Safety. We know that calcium is beneficial for the strength of our bones, however, use of shark cartilage may contribute to hypercalcemia (too much calcium in the blood), which may have deleterious effects on overall bone health. Some clinical evidence reports safety of use in specific populations when taken up to 24 weeks (possibly even up to 40 months) however pregnant and nursing women are advised to avoid shark cartilage and its use
is not recommended for children.

The Bottom Line. The above information summarized the history of use of shark cartilage as a supplement but does not constitute a recommendation for its use. As always, EN recommends consulting with your doctor before beginning any new supplement or nutritional product.

 —Andrea Giancoli, MPH, RD

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