Vitamin K
What is Vitamin K?
Vitamin K is an essential nutrient that plays a vital role in the process of maintaining normal blood coagulation (clotting) and bone metabolism [1].
There are two naturally occurring forms of vitamin K in the diet: phylloquinone (vitamin K1) and menaquinone (vitamin K2) [1].
Vitamin K1 is commonly found in leafy greens and is considered the main form of vitamin K in the diet.
Vitamin K2 is primarily synthesized by bacteria in the gut and can be obtained from meat, dairy, and fermented food products [2].
Since vitamin K is fat-soluble, it is better absorbed in the body when consumed with a fat source.
However, the body has a limited ability to store vitamin K [3]. Because of this, regular dietary intake of the vitamin is crucial to maintain adequate levels.
Research has shown that supplementation with vitamin K is potentially beneficial in improving the nutritional and metabolic status of children with autism, especially those with low levels of the vitamin [4].
Food Sources of Vitamin K
Vitamin K1 can be found in the highest amounts within plants and some oils [1]. Examples include:
Green leafy vegetables, such as:
Collard greens
Spinach
Some vegetable oils
Vitamin K2 is present in various animal-based and fermented foods [1]. These include:
Recommended Intake
Unlike most other vitamins, vitamin K does not have a Recommended Dietary Allowance (RDA). Instead, experts have established Adequate Intakes (AIs) - the amount assumed to ensure nutritional adequacy - for all ages based on usual vitamin K intakes in healthy populations [1].
Males
0-6 months: 2 μg*/d
7-12 months: 2.5 μg/d
1-3 years: 30 μg/d
4-8 years: 55 μg/d
9-13 years: 60 μg/d
14-18 years: 75 μg/d
19+ years: 120 μg/d
Females
0-6 months: 2 μg/d
7-12 months: 2.5 μg/d
1-3 years: 30 μg/d
4-8 years: 55 μg/d
9-13 years: 60 μg/d
14-18 years: 75 μg/d
19+ years: 90 μg/d
*μg is the scientific abbreviation for “microgram”
Deficiency
Vitamin K deficiency in adults is rare within the United States. However, the risk of deficiency is higher in newborn infants due to the low vitamin K content of breastmilk [5].
Symptoms of deficiency may include [5]:
Excessive bleeding from open wounds
Easy bruising and mucosal (nose, mouth) bleeding
Internal hemorrhaging
Individuals at increased risk for vitamin K inadequacy include [5]:
Those with restrictive diets and poor intake of vitamin K food sources
Individuals with fat malabsorption disorders, including inflammatory bowel disease and cystic fibrosis
Those taking a drug that interferes with vitamin K metabolism
Newborns who are exclusively breast-fed
Toxicity
Dietary Vitamin K1 is not toxic, even when consumed in large amounts. However, a synthetic, water-soluble vitamin K precursor called menadione can cause toxicity and should not be used to treat vitamin K deficiency. Due to the low potential for toxicity, no tolerable upper limit has been established [1].
Supplements
Supplemental vitamin K is widely available in the forms of tablets, capsules, and softgels, and can be found in most multivitamin/mineral supplements. Supplements containing vitamin K alone are also available. Many forms of vitamin K are used in supplements, including vitamin K1 and vitamin K2 [1]. The supplements will tell you the amount and the percentage of each on the supplement facts label. Vitamin K is also often combined with Vitamin D in supplemental form as it can optimize absorption of both.
Examples
Liquid
Capsules
Gummies
Note: All supplements are linked to Amazon for convenience, however, buying supplements on Amazon does not guarantee quality, as there are many “unverified resellers” selling nutrition supplements. To buy supplements that are verified to be sent directly to the consumer, you can create an account on the Autism Dietitian FullScript and search for the respective supplement under “Catalog”.
DISCLAIMER: Before starting any supplement or medication, always consult with your healthcare provider to ensure it is a good fit for your child. Dosage can vary based on age, weight, gender, and current diet.
Vitamin K & Autism in the Research
Deficiency
Children with autism are more likely to have a vitamin K deficiency than typically developing children [6].
Decreased levels of vitamin K in the body might be linked to autism neuropathology [7].
Autism Severity
Oral supplementation of vitamin K was found to be beneficial in improving the nutritional and metabolic status in children with autism [3].
Maternal Vitamin K
Low levels of maternal and neonatal vitamin K may be associated with increased susceptibility to neurodevelopmental disorders including autism [8].
Bone Health
Adequate vitamin K intake was associated with a significant increase in bone mineral content and bone mass in adolescents [9].
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[1] National Institutes of Health Office of Dietary Supplements. Vitamin K. National Institutes of Health; 2013. Available from: https://ods.od.nih.gov/factsheets/vitaminK-HealthProfessional/#en1
[2] Walther B, Karl JP, Booth SL, Boyaval P. Menaquinones, bacteria, and the food supply: the relevance of dairy and fermented food products to vitamin k requirements123. Adv Nutr. 2013;4(4):463-473.
[3] Micronutrient Information Center. Vitamin K. Oregon State University Linus Pauling Institute; 2001. Available from: https://lpi.oregonstate.edu/mic/vitamins/vitamin-K#vitamin-K-oxidation-reduction-cycle
[4] Adams JB, Audhya T, McDonough-Means S, et al. Effect of a vitamin/mineral supplement on children and adults with autism. BMC Pediatrics. 2011;11(1):111.
[5] Truong JT, Booth SL. Emerging issues in vitamin k research. J Evid Based Complementary Altern Med. 2011;16(1):73-79.
[6] Bjørklund G, Waly MI, Al-Farsi Y, et al. The role of vitamins in autism spectrum disorder: what do we know? J Mol Neurosci. 2019;67(3):373-387.
[7] Ribeiro R, Nicoli JR, Santos G, Lima-Santos J. Impact of vitamin deficiency on microbiota composition and immunomodulation: relevance to autistic spectrum disorders. Nutritional Neuroscience. 2019;0(0):1-13.
[8] Lee BK, Eyles DW, Magnusson C, et al. Developmental vitamin D and autism spectrum disorders: findings from the Stockholm Youth Cohort. Molecular Psychiatry. Published online November 6, 2019:1-11.
[9] Karpiński M, Popko J, Maresz K, Badmaev V, Stohs SJ. Roles of vitamins d and k, nutrition, and lifestyle in low-energy bone fractures in children and young adults. J Am Coll Nutr. 2017;36(5):399-412.
Authors
Brittyn Coleman, MS, RDN/LD, CLT
April Allen, Dietetic Intern
Laura Flournoy, Dietetic Intern
