New FFQ can assess vitamin K intake in Mediterranean populations

The authors from Faro, Portugal, found that their final FFQ which included 54 food items, explained 90% of vitamin K intake.

Vitamin K and the Mediterranean population​ 

Vitamin K​ is crucial for maintaining human health and deficiency has been associated with age-related diseases. 

Previous studies​ have highlighted the multifaceted functions of vitamin K in various body tissues and processes, including blood coagulation, cardiovascular health, bone health, anti-inflammatory effects, antioxidant properties, and cognitive promotion.

Vitamin K exists in two forms, vitamin K1 (VK1) and vitamin K2 (VK2), with different dietary sources and activities.

While VK1 is mainly obtained from green leafy vegetables, VK2 is derived from fermented foods, meat, and dairy products.

As the authors of the new study note, existing FFQs for assessing vitamin K intake were not suitable for a Mediterranean population due to differences in dietary patterns as they are based on American populations. 

Vitamin K has a recommended daily intake (RDI) based on the median intake of VK1 in American adults​, set at 120 μg/day for men and 90 μg/day for women.

However, in Europe, 75 μg vitamin K has been recommended as daily allowance​.

The authors explain: “A Mediterranean population traditionally follows an eating pattern where vitamin K-rich foods, such are leafy green vegetables and different types of cheeses, are frequently consumed.” 

The newly developed FFQ aimed to capture the intake of both VK1 and VK2, providing a valuable tool for evaluating vitamin K intake in this specific population.

Significance​

The authors state: “Most FFQs developed to estimate the dietary consumption of vitamin K have specifically focused on VK1 mainly because, in the Western diet, it accounts for nearly 90% of total vitamin K intake​.

“However, accumulating evidence from basic research and clinical studies has highlighted the health-beneficial effects of VK2, particularly due to its long half-life and extrahepatic distribution.” 

They explain that while VK1 is preferentially accumulated in the liver​ and is poorly retained in the organism with a half-life time of 1–2 h, VK2 has a half-life time of 68 h and is available to extrahepatic tissues through circulation, resulting in increased bioavailability​ of the whole body.

They additionally note that in terms of functionality, VK2 (particularly MK-7 and MK-4) has been shown to have a higher bioactivity than VK1 in different molecular processes, such as gamma-glutamylcarboxylation cofactor​, inhibitory effect on bone resorption​, antioxidant properties,​ the activation of sphingolipid metabolism​, and anticancer qualities.​ 

The authors suggest that “VK2 is the major active form of vitamin K, accounting for 70% of total extrahepatic activity, while VK1 contributes only 5%, and that the beneficial effects of VK2 are not covered by current RDI guidelines,​” noting the importance for an evolved FFQ.  

The study​

The prospective study was conducted in a non-random sample of 38 healthy adult volunteers.

The FFQ was designed based on a validated Portuguese FFQ used in nationally representative studies and on literature reviews, to include foods containing ≥5 μg of vitamin K/100 g and foods with a lower vitamin K content, yet commonly included in a Mediterranean diet.

Vitamin K intake was estimated from 24h recalls and six days of food records, and the final design of the FFQ included 54 food items which, according to regression analyses, explains 90% of vitamin K intake.

The authors note: “Mean differences in vitamin K intake based on food records (80 ± 47.7 μg/day) and on FFQ (96.5 ± 64.3 μg/day) were statistically non-significant. Further, we found a strong correlation between both methods (r = 0.7; p​ = 0.003).” 

The authors concluded: “Our study allowed the development of a valid FFQ for the assessment of vitamin K intake in a sample of Portuguese adults, with a very low cost of administration and processing, and with low respondent burden.” 

The authors do however mention: “It should be noted that MK-4 is a result of vitamin K conversion​ and is dependent from VK1 intake​ and that MK-4 is present in most extrahepatic tissues.​ In this context, more attention should be given to the dietary intake of both VK1 and VK2​.”

Journal: Nutrients

https://www.mdpi.com/2072-6643/15/13/3012​

“New Food Frequency Questionnaire to Estimate Vitamin K Intake in a Mediterranean Population”

Authors: Ezequiel Pinto, Carla Viegas, Paula Ventura Martins, Tânia Nascimento, Leon Schurgers and Dina Simes.