Vitamin K
Vitamin K supports normal blood clotting and bone-related proteins. Food-first intake is preferred; supplements should be matched to diet, health context, and safety considerations.
Overview
Biological role
Vitamin K supports normal blood clotting and bone-related proteins.
Mechanism of action
Vitamin K contributes to normal physiology through nutrient-specific enzyme, structural, signaling, transport, or regulatory roles described in authoritative nutrition references.
Chemical forms
Vitamin K may appear in foods and supplements in different chemical forms. Selection should consider the nutrient form, dose, tolerance, and health context.
Quick answers before choosing a supplement
Chemical forms and absorption
Common forms
Vitamin K may appear in foods and supplements in different chemical forms. Selection should consider the nutrient form, dose, tolerance, and health context.
Absorption context
Absorption can vary with food composition, supplement form, dose, and timing. Food-first intake is preferred when possible.
Clinical use
Established essential nutrient roles should be separated from supplement benefit claims. Supplement use is most appropriate when there is inadequate intake, increased need, deficiency risk, or a clinical indication.
Absorption and action pathway
What to take with, and what to avoid
Works Well With
Avoid / Use Caution
Best time to take
Frequently asked questions
When is the best time to take Vitamin K?
Take consistently; fat-soluble vitamins are usually best with a meal that contains fat, while water-soluble vitamins are usually flexible.
Can Vitamin K be taken with coffee or milk?
It depends on the vitamin. Fat-soluble vitamins are best with food; water-soluble vitamins are generally more flexible.
Who should be careful with Vitamin K?
Pregnant or lactating people, older adults, children, people with chronic diseases, and people taking regular medicines should use supplements with professional guidance.
Food and Intake
| Age / group | Male | Female | Pregnancy | Lactation | Upper limit |
|---|---|---|---|---|---|
| 1-3 years | 30 | 30 | – | – | not established |
| 4-8 years | 55 | 55 | – | – | not established |
| 9-13 years | 60 | 60 | – | – | not established |
| 14-18 years | 75 | 75 | 75 | 75 | not established |
| 19+ years | 120 | 90 | 90 | 90 | not established |
International reference intake comparison
| Country / authority | Common reference value |
|---|---|
| USA / NIH-FNB | AI 120/90 mcg men/women; no UL established |
| Europe / EFSA | AI 70 mcg adults based on phylloquinone |
| Australia-New Zealand / NRV | AI about 70/60 mcg men/women |
| Thailand / Thai FDA | Thailand: use Thai RDI and Thai FDA / Ministry of Public Health regulations for labeling and supplement products. Do not interpret labeling values as therapeutic doses; product-specific limits must be checked against the latest notification and formula. |
This table compares reference-intake frameworks across authorities. Values may use different terms such as RDA, AI, PRI, or NRV and should not be merged into one universal dose.
Food source comparison for Vitamin K
| Food | Serving amount | Vitamin K | %DV | %DV bar | Servings to reach 120 mcg |
|---|---|---|---|---|---|
| cooked collard greens | 1/2 cup | 530 mcg | 442% | 0.2 | |
| cooked turnip greens | 1/2 cup | 426 mcg | 355% | 0.3 | |
| raw spinach | 1 cup | 145 mcg | 121% | 0.8 | |
| raw kale | 1 cup | 113 mcg | 94% | 1.1 | |
| cooked broccoli | 1/2 cup | 110 mcg | 92% | 1.1 | |
| soybean oil | 1 tablespoon | 25 mcg | 21% | 5 |
Food values are practical comparison values. Actual content varies by variety, preparation, fortification, and serving size.
Safety
Deficiency
Inadequate Vitamin K intake or absorption may affect body systems related to normal blood clotting and bone-related proteins. Deficiency risk depends on diet, absorption, medical conditions, and life stage.
Excess and toxicity
People taking warfarin or similar medicines should keep intake consistent and ask a clinician.
Precautions
People taking warfarin or similar medicines should keep intake consistent and ask a clinician.
Special populations
Pregnant or lactating people, older adults, children, people with chronic diseases, and people taking regular medicines should use supplements with professional guidance.
Fast risk map
LOW: insufficient intake
Inadequate Vitamin K intake or absorption may affect body systems related to normal blood clotting and bone-related proteins. Deficiency risk depends on diet, absorption, medical conditions, and life stage.
UL: excess intake
People taking warfarin or similar medicines should keep intake consistent and ask a clinician.
Precautions: interactions and timing
People taking warfarin or similar medicines should keep intake consistent and ask a clinician.
SP: special populations
Pregnant or lactating people, older adults, children, people with chronic diseases, and people taking regular medicines should use supplements with professional guidance.
Interactions and Clinical Context
Drug interactions
Potential interactions depend on the nutrient, supplement dose, medicines used, and medical conditions. People using regular medicines should check interaction guidance from clinical sources or ask a clinician.
Food interactions
Absorption can vary with food composition, supplement form, dose, and timing. Food-first intake is preferred when possible.
Clinical notes
Established essential nutrient roles should be separated from supplement benefit claims. Supplement use is most appropriate when there is inadequate intake, increased need, deficiency risk, or a clinical indication.
Evidence level
High for essential nutrient role; nutrient-specific supplementation benefits depend on baseline status and clinical context.