Capillaries are tiny blood vessels that connect arteries and veins. They form dense networks throughout the body to supply tissues and organs with oxygen and nutrients. Weak and leaky capillaries can cause a variety of health issues. Some claim vitamin K plays a role in strengthening capillaries, but does the evidence support this?
What are capillaries?
Capillaries are the smallest blood vessels in the body, with internal diameters of only 5-10 micrometers. This is small enough for red blood cells to pass through in single file. The walls of capillaries consist of a thin, single layer of endothelial cells. There are no smooth muscle cells like in arteries and veins.
Capillaries provide the critical link between arteries and veins. Oxygen and nutrients diffuse from the blood in capillaries into surrounding tissues. Waste products also diffuse from tissues into capillaries for removal. Capillaries are vital for maintaining normal function and health.
Capillary networks
Capillaries form extensive networks throughout the body. They come into intimate contact with nearly every living cell. The total length of all capillaries in the adult human body is estimated at 95,000 km. If laid end to end, this could circle the Earth more than twice.
Density of capillary networks varies depending on the metabolic needs of tissues. Networks are dense in vital organs like the brain, heart, liver and kidneys. Other tissues like fat and cartilage have less dense networks. Arterioles can control blood flow into capillary networks to match local metabolic needs.
Exchange of substances
Diffusion allows the efficient exchange of gases, nutrients and waste products between blood and tissues:
– Oxygen diffuses from red blood cells into tissues
– Carbon dioxide diffuses from tissues into blood for removal
– Glucose, amino acids and other nutrients diffuse from blood into tissues
– Metabolic wastes diffuse from tissues into blood for filtration and excretion
The thin walls and slow flow through capillaries provides optimal conditions for diffusion. Red blood cells release oxygen as they squeeze through tight capillaries.
What causes weak and leaky capillaries?
While capillaries are extremely narrow, their walls normally provide an intact barrier between blood and tissues. However, capillaries can sometimes become weak and leaky. This allows fluids and proteins to seep out into surrounding tissues. It also allows entry of toxins and pathogens that can trigger inflammation.
There are several factors that can cause capillaries to become weak and permeable:
Aging
Aging naturally weakens capillaries. As endothelial cells age, they become enlarged and have more gaps between them. Connective tissues supporting capillaries also weaken with age. This makes them more fragile and prone to leakage.
High blood pressure
Chronic high blood pressure inflicts shear stress on capillary walls. This can damage the endothelial lining. Hypertension is a major risk factor for leaky capillaries.
Diabetes
Elevated blood glucose in diabetes inflicts chemical damage to endothelial cells. This weakens capillary integrity. Diabetes also impairs growth of new capillaries, which is needed for repair.
Inflammation
Inflammatory chemicals generated during infections, autoimmune disorders and diseases like obesity can impair endothelial function. Inflamed endothelial cells retract and form gaps between cells, allowing fluid and proteins to leak out.
Nutrient deficiencies
Deficiencies in certain vitamins and minerals needed for endothelial health may contribute to weakened capillaries. This includes vitamin C, vitamin D, folate and zinc.
Signs and symptoms of leaky capillaries
Leakage from fragile capillaries can manifest in several ways:
Edema
Fluid and proteins leaking from capillaries into surrounding tissues causes edema (swelling). Edema is most common in the lower legs and feet due to effects of gravity. But it can occur anywhere. Generalized edema all over the body is a sign of serious capillary leakage.
Easy bruising
Capillary leakage into skin can cause unexplained or easy bruising. Minor bumps that shouldn’t cause bruising may result in large bruise areas. These are often signs of low platelet counts and fragile capillaries.
Red spots
Tiny red spots on skin called petechiae are due to localized bleeding from leaky capillaries into skin. These differ from a rash since they don’t itch or inflame the skin. Petechiae spots can range from pinpoint size to a few millimeters.
Rosacea
Rosacea is characterized by chronic facial redness and flushing. Leaky and overloaded capillaries are thought to play a central role in rosacea. Damaged capillaries allow plasma proteins to accumulate in skin, triggering inflammation.
Varicose veins
While not usually caused by capillary leakage, varicose veins in the legs result from weakened blood vessels that allow blood to pool and flow backwards. They are associated with edema, easy bruising and leg ulcers – all linked to fragile capillaries.
Does vitamin K play a role in capillary health?
Vitamin K is emerging as an important nutrient for maintaining the health and integrity of blood vessels, including capillaries. Here’s an overview of vitamin K and what science says about its effects on capillaries:
What is vitamin K?
Vitamin K is fat soluble vitamin that exists in two main forms:
– Vitamin K1 (phylloquinone): Found in green leafy vegetables and some oils
– Vitamin K2 (menaquinones): Synthesized by bacteria in the gut and fermented foods
K1 is the main form obtained in the diet, while K2 depends more on gut bacteria. Vitamin K acts as a cofactor for enzymes that activate proteins involved in calcium metabolism and blood clotting. More recent evidence shows it also supports vascular health.
Vitamin K and vascular calcification
Vascular calcification is the hardening of blood vessels through build up of calcium deposits in soft tissues. It stiffens blood vessels and impairs flexibility. Vitamin K prevents calcification by activating matrix Gla protein (MGP), which inhibits calcium deposition in vessel walls.
Vitamin K deficiency
Suboptimal vitamin K intake is common. Deficiency causes undercarboxylation of MGP, allowing vascular calcification to progress. Studies show people with the lowest vitamin K status have up to a 50% higher risk of cardiovascular disease. Boosting intake may suppress calcification.
Vitamin K and endothelial function
Endothelial cells lining all blood vessels depend on vitamin K. Human studies find vitamin K2 supplements improve endothelial function and reduce stiffness of arteries. Animal studies also show vitamin K protects endothelial cells from oxidative damage. This suggests an important role in maintaining capillary integrity.
Vitamin K and inflammation
Chronic low grade inflammation damages capillaries over time. Vitamin K inhibits activation of a pro-inflammatory transcription factor called NF-kB. This may help protect capillaries from inflammatory damage.
Vitamin K and edema
A study in dialysis patients with edema found that vitamin K2 supplements reduced leakage of fluid into leg tissues. The reduction in capillary permeability was attributed to vitamin K protecting endothelial cell function.
Overall, evidence indicates vitamin K protects and preserves the health of endothelial cells lining capillaries and other vessels. Ensuring adequate intake may strengthen capillaries against leakage.
Recommended intake of vitamin K
The recommended adequate intake (AI) for vitamin K according to the National Institutes of Health is listed below:
Infants
– 0 to 6 months: 2 mcg/day
– 7 to 12 months: 2.5 mcg/day
Children and teens
– 1 to 3 years: 30 mcg/day
– 4 to 8 years: 55 mcg/day
– 9 to 13 years: 60 mcg/day
– 14 to 18 years: 75 mcg/day
Adults
– 19+ years: 90 mcg/day for women; 120 mcg/day for men
Pregnancy and breastfeeding
– Pregnant women: 90 mcg/day
– Breastfeeding women: 90 mcg/day
These AIs are based on typical vitamin K intakes that are believed to maintain adequate blood coagulation. However, some experts suggest higher intakes may be optimal for vascular health. Consistently getting the AI from diet alone can be challenging.
Dietary sources of vitamin K
The main dietary sources of vitamin K1 (phylloquinone) include:
| Food | Serving | Vitamin K1 (mcg) |
|---|---|---|
| Kale, cooked | 1 cup | 531 |
| Spinach, cooked | 1 cup | 444 |
| Collards, cooked | 1 cup | 418 |
| Turnip greens, cooked | 1 cup | 265 |
| Broccoli, cooked | 1 cup | 220 |
| Brussels sprouts | 1 cup | 219 |
| Romaine lettuce | 1 cup | 57 |
| Asparagus | 6 spears | 22 |
The main dietary sources of vitamin K2 (menaquinones) include:
| Food | Serving | Vitamin K2 (mcg) |
|---|---|---|
| Natto | 1 oz | 1020 |
| Hard cheese | 1 oz | 12 |
| Egg yolk | 1 large | 6 |
| Butter | 1 tbsp | 5 |
| Chicken liver | 3 oz | 3 |
Key points
– Dark leafy greens provide the most vitamin K1 per calorie
– Natto is the richest dietary source of vitamin K2
– Gut bacteria synthesize vitamin K2, providing another source
– Low fat diets provide less vitamin K2 since it’s fat soluble
Vitamin K supplementation
While dietary vitamin K should be prioritized, supplements may help those at risk for deficiency get adequate intake. Here are some key points about vitamin K supplementation:
– Vitamin K2 supplements may be better utilized than K1
– Doses of 50-200 mcg/day of K2 have improved vascular markers in studies
– Consult your doctor before supplementing if taking blood thinning medication
– MK-4 and MK-7 are common supplemental forms of K2
– Vitamin K2 is best taken with a fat source to enhance absorption
For capillary health, getting an adequate amount of vitamin K1 from leafy greens plus a vitamin K2 supplement provides a comprehensive approach. Testing vitamin K levels can help determine individual needs.
Other ways to strengthen capillaries
In addition to vitamin K, other evidence-based ways to promote capillary health include:
Exercise
Regular exercise improves endothelial function and stimulates growth of new capillaries. But avoid excessive exercise which causes capillary damage.
Blood pressure control
Keeping blood pressure in a healthy range reduces mechanical strain on capillary walls. Lifestyle changes and medication can both help control high blood pressure.
Blood sugar control
Preventing blood sugar spikes through diet, exercise, sleep and medication preserves capillaries in those with diabetes or insulin resistance.
Stress reduction
Chronic stress and elevated cortisol negatively affect endothelial function. Yoga, meditation and other relaxation practices counter these effects.
Smoking cessation
Quitting smoking allows capillaries to regrow and strengthen. Smoking seriously damages capillary networks.
Healthy diet
Eating a diet rich in fruits, vegetables, whole grains, nuts/seeds and fatty fish provides antioxidants and polyphenols that protect capillaries.
Conclusion
Preserving healthy capillaries is crucial for ensuring normal organ function. Emerging evidence suggests vitamin K plays an important role in maintaining capillary integrity through protecting endothelial cells, reducing calcification, inhibiting inflammation and possibly other mechanisms.
Adequate vitamin K1 intake from leafy greens along with a vitamin K2 supplement provides a comprehensive dietary approach. Combining this with other lifestyle factors like exercise, stress reduction and a healthy diet offers multiple layers of defense against capillary leakage and its detrimental effects.
While more human studies on vitamin K’s effects on capillaries are still needed, current evidence supports the potential for vitamin K sufficiency to strengthen these vital small blood vessels.