Vitamins are good for us
Some vitamins covet the stage of public awareness and rarely relinquish the limelight. If not consumed in sufficient quantities, they threaten dire health consequences for nonbelievers, children and small noisy dogs. Other vitamins, like vitamin K, are lost in the extrovert vitamin ABCD crowd and struggle to be heard. Their message, however, is equally profound for good health in humans. The paradox is that vitamin deficiency remains for many people a significant health and nutrition issue even in the presence of an abundance of food. Moreover, scientists continue to discover new biological roles of vitamins and new food sources containing different molecular forms of known vitamins, which together cause the regular revision of recommended daily intake levels.
Recent investigations that expanded the known biological roles and molecular forms of vitamin K are a case in point, with several studies highlighting additional potential benefits to people that may not be realized because of current dietary and nutrition practices. A recent study published in Current Developments in Nutrition and authored by Fu and colleagues reported that full-fat dairy products contain multiple forms of a poorly characterized form of vitamin K—vitamin K2—and other studies reveal unexpected roles of this vitamin subtype in maintaining bone and cardiovascular health.
What is a Vitamin?
Scientists discovered most vitamins many decades ago when they noticed that some specific diets consumed routinely by humans and animals caused severe illnesses. The scientists reasoned that food components critical for good health were missing in these diets. They identified these food components (containing vitamins) and added them into the deficient diets, thereby preventing these illnesses. Subsequently, the molecular form of each vitamin was characterized. Vitamins are small organic molecules that cannot be synthesized by the body, and therefore, they must be obtained from external sources such as food or in the case of vitamin D, sunlight. Typically, very low quantities of vitamins are essential for key biochemical reactions that underpin normal cellular metabolism and function. The Nobel Committee recognized the immense importance of vitamins to human health with the award of a total of nine ‘Nobel prizes’ between 1929 and 1964.
Vitamin K, with its multiple forms, is among the lesser-known nutrients. Vitamin K, which helps the blood to clot, is most commonly thought to have originated from leafy greens such as spinach, kale and broccoli. Dietary sources of vitamin K are found in two natural forms: phylloquinone (PK, or vitamin K1), which is widely distributed through plant-based foods, and menaquinones (MK, or vitamin K2), which appear to be primarily in animal products and fermented foods. Almost all MK forms are also produced by bacteria in the human gut. Not much is known about MK amounts in U.S. dairy products.
“Dairy foods contain minute amounts of PK, the best known of the vitamin K forms, and so dairy is not commonly considered a rich dietary source for this nutrient. However, when it comes to MK forms, we found that dairy items already found in many peoples’ refrigerators are indeed a good dietary source for vitamin K,” said Xueyan Fu, Ph.D., first and corresponding author and scientist in the Vitamin K Laboratory at the USDA HNRCA.
Guidelines for adequate vitamin K intake are based only on PK intake without consideration of other forms of vitamin K. MK differs from PK in structure in that they are compounds with different numbers of isoprenoid units in the side chain, designated as MK4 through MK13. Which forms of MK are present reflects which bacteria might be in the dairy products. Lactic acid bacteria, for example, are widely used in dairy and fermented foods.
Functions and Sources of Vitamin K
The Danish scientist Henrick Dam discovered vitamin K nearly 90 years ago. He noticed that low-fat diets in chickens led to bleeding tendencies that could be prevented when normal levels of fat (containing vitamin K) were restored in the diet. Since then vitamin K has been recognized by nutritionists as a fat-soluble dietary component essential for normal blood coagulation in humans. Dam later discovered that the vitamin K required for blood clotting existed in two related molecular forms, phylloquinone (vitamin K1) and menaquinone (vitamin K2). Vitamin K1 is prevalent in leafy green vegetables and has been well characterized. Vitamin K2 is present in meat, eggs, and dairy products, but as Fu and colleagues noted, historically vitamin K2 has been poorly studied in terms of its functions, multiple structures and abundance in different foods. Additional molecular versions of vitamin K2 are also produced by microbial fermentation, and these are found in some cheeses and nattō, a Japanese delicacy consisting of fermented soybeans.
Multiple Forms of Vitamin K are Present in Dairy Products
Many people know dairy foods are an important source of nutrients for growing children and teens. Milk and other dairy foods, however, are great sources of protein, calcium and vitamins for people in all walks of life, including adults, seniors and athletes. Dairy products are loaded with essential vitamins and minerals, including carbohydrates, protein, calcium, phosphorus, potassium, vitamins A, D, B12, riboflavin and niacin.
Just one 8-ounce serving of milk has 8 grams of protein, which builds and repairs muscle tissue (an equal serving of almond beverage has only 1 gram of protein). One serving of milk also meets the daily values (DV) for the following nutrients (based on Food and Drug Administration guidelines):
Fu and colleagues used an extremely powerful and sensitive technique, mass spectrometry, to characterize the various forms of menaquinones and phylloquinone in a range of US dairy products. Detectable but only small quantities of phylloquinone (vitamin K1) were present in full-fat dairy products. The investigators demonstrated that three molecular forms of menaquinone (different sized versions of vitamin K2) were present in “appreciable amounts” in full-fat dairy products. Importantly, Fu and colleagues showed that reduced-fat or fat-free dairy products contained only 5–22% of the total vitamin K content of the full-fat dairy products. The investigators concluded that the total vitamin K contents of various dairy products are relatively high and in proportion to the fat content of the product. They speculated that the multiple forms of menaquinones found in full-fat milk may be indirectly derived from microbial fermentation occurring in the specialized ruminant digestive system of the cow.
In a summary
A vitamin K deficiency is serious and can lead to a range of health issues. Even getting less than the recommended dosage over a prolonged period may be bad for a person’s overall health, and could lead to some severe problems. Getting both vitamin K-1 and K-2 in the diet is essential for ideal overall health, and some foods make it easy to hit the daily-recommended values.
Incorporating every food containing vitamin K is not necessary, but it is helpful to know which foods contain the vitamin to be sure the body gets enough each day. On the other hand, people taking anticoagulants or the blood-thinning medications should be cautious about consuming too much vitamin K. People taking these medications should speak to a doctor about their vitamin K levels. For people taking medication, knowing which foods contain high sources of vitamin K is the best way to avoid them. However, the most important thing is keeping the levels of vitamin K consistent each day.