Both vitamins K and D are fat-soluble nutrients both of which play a role in calcium metabolism. Vitamin D deficiency (VDD) is widespread and has become a major healthcare issue. The prevalence of VDD is estimated to be more than a billion people worldwide. It has been reported in individuals with CKD, VDD is as high as 80%. Vitamin K functions as a cofactor for the enzyme γ-glutamyl carboxylase (GGCX), this activates vitamin K dependant proteins (VKDPs) which are involved in haemostasis, and vascular and bone health. We understand vitamin K plays a key role in blood coagulation; however, research suggests vitamin K‐dependent proteins (VKPDs) are important in the regulation of tissue calcification which affects bones and arterial vessel walls. Research has found a deficiency in vitamin K has been associated with increased calcium deposition and coronary artery calcification, which can lead to cardiovascular disease. We now have accumulated evidence that patients with CKD suffer from a subclinical vitamin K deficiency.
Food sources of Vitamin K 1
Vitamin K is the generic name for a family of compounds that hold a common chemical structure 2-methyl-1,4-naphthoquinone. It is naturally present in some foods and is also be found as a supplement.
Vitamin K is a group of compounds that are divided into two groups-
- K1 (phylloquinone) and K2 (menaquinone).
Vitamin K1 is the most common form which is mainly found in plant foods and dark leafy greens. Vitamin K2 is also found in fermented plant foods such as natto a fermented soybean dish and in some animal foods.
Following are some good food sources of vitamin K:
- Cooked spinach
- Cooked kale
- Cooked mustard greens
- Cooked collard greens
- Cooked beet greens
- Raw swiss chard
- Raw dandelion greens
- Cooked turnip greens
- Cooked cabbage
- Dried basil, sage, marjoram, thyme, oregano, fresh parsley, chives and dried coriander
Food sources of Vitamin K 2
- Goose liver
- Beef liver
- Soft cheese
- Blue cheese
- Hard cheese
- Full-fat milk
Symptoms of Vitamin K deficiency
The bacteria in your gut will produce some of the vitamin K your body requires. Vitamin K deficiency is rare in healthy adults, however, if you do have a deficiency, you are more likely to bruise and bleed easily, and it can also make periods heavier. It may also be more difficult for your body to stop bleeding after an injury or an operation.
Serious health concerns are more likely to cause a deficiency, these include:
- Cystic fibrosis
- Digestive disorders that cause an issue with fat malabsorption
- Blocked bile duct
- Medication such as warfarin and taking antibiotics over a long duration of time may also cause a deficiency of vitamin K.
Our bodies produce vitamin D when we are exposed to sunlight, however, there are some common reasons why it is difficult to get vitamin D in this way. As we have become a lot more sun smart to reduce the risk of skin cancer, we cover up, wear sunscreen and avoid being out in the sunlight during peak UV times, depending on where you live in the world sometimes it’s just not possible to have enough year-round exposure. This is why supplementation and food sources are important.
Sources of Vitamin D
- Wild caught salmon
- Cod liver oil
- Canned tuna
- Egg yolk
Causes of Vitamin D Deficiency
- Reduced synthesis of cholecalciferol in the skin-Reduced sun exposure can be due to veiling, illness, having darker skin, aging or immobility (staying indoors). As we age, our ability to synthesize cholecalciferol from sun exposure decreases.
Disorders of Malabsorption
- Small bowel disorders such as coeliac disease, inflammatory bowel disease, and disorders such as lymphoma, and granuloma can cause malabsorption of vitamin D. Pancreatic disorders or biliary obstruction can also have the same effect.
Enhanced Degradation of 25-hydroxyvitamin D
- Medications such as anticonvulsants and rifampicin increase the degradation of vitamin D, which can contribute to or exacerbate vitamin D deficiency.
- Other medications such as laxatives, steroids (prednisolone), orlistat (weight loss medication), cholesterol-lowering drugs and seizure-preventing drugs can also lower vitamin D levels.
- Having a body mass index higher than 30 is associated with lower levels of vitamin D, in these cases, higher doses of vitamin D are required to help maintain and reach optimal/normal levels.
Kidney & Liver Disease
- The body is required to change vitamin D into a form that can be absorbed. Kidney and liver disease reduces the amount of hepatic enzyme 25–hydroxylase from your liver and 1-alpha-hydroxylase from your kidneys, a lack of these enzymes leads to lower levels of active vitamin D in the body.
Signs & Symptoms of Vitamin D Deficiency
A severe lack of vitamin D in children causes Rickets. A slight deficiency is not usually obvious and you may not experience signs or symptoms. However, signs and symptoms may include:
- Bone pain
- Mood changes such as depression
- Muscle weakness, cramping or muscle aches can be present
Vitamin D deficiency has been found to increase the progression of CKD. This may be due to a number of factors including:
- Reduced exposure to sunlight
- Proteinuria (loss of protein in urine)
- Reduced skin synthesis of vitamin D
- Decreased intake of vitamin D-rich foods
- Decreased physical activity
Another important factor linked with vitamin D deficiency in those with kidney disease is related to reduced kidney function, as the final stage of converting vitamin D into its active form calcitriol occurs in the kidneys. So when kidney function declines there is a progressive decline in the activity of 1-alpha hydroxylase, which is the enzyme required to convert vitamin D to its active form.
Vitamin K & Vitamin D for Cardiovascular Health
Atherosclerosis is one of the main issues thought to cause cardiovascular disease (CVD). Atherosclerosis is where the arteries become blocked by plaque or atheromas, this can cause CVD when arteries become completely clogged by a blood clot or when a narrowed artery restricts the flow of blood. This, in turn, limits the amount of oxygen and blood reaching organs or tissue. Smoking, high cholesterol, obesity, hypertension and a sedentary lifestyle can accelerate the disease process.
Matrix Gla-protein (MGP) is a vitamin K-dependent protein that may play a role in the prevention of vascular calcification. MGP’s full function is still unclear, animal data has suggested inadequate vitamin K levels can lead to undercarboxylated MGP, which may increase vascular calcification, increasing the risk of coronary heart disease. This is important information for those with CKD as the rates of vascular calcification are much higher in these patients than those of the general population.
We understand vitamin K plays a key role in blood coagulation; however, research suggests vitamin K‐dependent proteins (VKPDs) are important in the regulation of tissue calcification which affects bones and arterial vessel walls. Research has found a deficiency of vitamin K has been associated with increased calcium deposition and coronary artery calcification, which can lead to cardiovascular disease.
Most clinical trials on vitamin D and K supplementation have been performed on post-menopausal women with bone health as the main focus. Few intervention trials have looked at vitamin D and K supplementation focusing on cardiovascular outcomes. However, current studies do suggest, taking Vitamin D and K together may be more effective than taking either one alone for bone or cardiovascular health.
Two trials studied the effect of vitamin D versus vitamin D and K in non-dialyzed CKD patients on cardiovascular risk factors and vascular calcification over a 9-month period. In the group with 42 CKD patients, the increase in carotid intima-media thickness (IMT) was lower in the vitamin K and D group compared to the D group alone. However, in another small trial (n=38), there were no differences shown between the D versus K and D groups on cardiovascular risk markers. Once again, it has been noted, very few clinical trials have been performed in this area and more need to be done to clarify the outcomes. Often these trials are combined with other micronutrients which, of course, makes it really difficult to pinpoint the sole effect of vitamin D and K alone. The limited studies do suggest that supplementing vitamin D and K for joint health, may also provide good cardiovascular support.
Vitamin K & Insulin Resistance
Research in this area has suggested vitamin K has been associated with insulin resistance. A 2008 study published in Diabetes Care found vitamin K supplementation for the duration of 36 months at a dietary dose may reduce the progression of insulin resistance in men. In one observational study, they found higher dietary and supplemental intake of vitamin K was associated with greater insulin sensitivity and a better glycaemic index.
So there it is, both vitamin D and K play an important role in the body. You can get your vitamin D levels checked through your doctor to get a better idea of where your level sits and if you need to supplement further.
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Until next time, take care.