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Background: The relationship between vitamin intake and depression has attracted increasing attention. However, several studies examining such relationship among populations at different age groups have produced inconsistent findings. This study was aimed to investigate the cross-sectional association between vitamin K intake and depressive symptoms in US adults.

Methods: We used the data from a nationally representative sample of 11,687 adults from the 2013 to 2018 National Health and Nutrition Examination Survey (NHANES). Vitamin K intake was assessed by the 24-h dietary recall at the first day. Depressive symptoms were assessed using the 9-item Patient Health Questionnaire (PHQ-9). Logistic regression and generalized additive model were used to examine the association between vitamin K intake and depressive symptoms.

Results: The weighted prevalence of depressive symptoms was 10.2% (8.0% in men and 12.0% in women). We observed a significant inverse linear relationship between vitamin K intake and depressive symptoms in models adjusted for age, sex, race/ethnicity, marital status, educational status, family poverty income ratio (PIR), home status, body mass index (BMI), smoking status, physical activity, sleep disorders, hypertension, hyperlipidemia, and diabetes. The odds ratios (OR) (95% CI) for the highest compared with the lowest quartile of vitamin K intake was 0.68 (95% CI: 0.52, 0.89, p-trend < 0.05). The association was similar in subgroups stratified by age, sex, race/ethnicity, marital status, educational status, PIR, home status, BMI, smoking status, physical activity, sleep disorders, hypertension, hyperlipidemia, and diabetes.

Conclusion: Vitamin K intake was inversely and independently associated with the odds of depressive symptoms in the US adults. Prospective studies are warranted to confirm our findings.

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Sorry for being stupid, but I assume the depressive symptoms come because of getting too little vitamin K and not the other way around?

All they present is a simple correlation so they can't say one variable causes the other. This is not a very good study. I have a feeling they looked at a bunch of variables and this one they found was statistically significant so they wrote a paper on it. I would not pay any attention to this finding unless you are researcher and can create a better study to explore this initial findings.

You have a feeling they found a significant variable? How else would you do it? Are you going to randomize people to eat or not eat green vegetables?

"We observed a significant inverse linear relationship between vitamin K intake and depressive symptoms"

Dietary recall is a bit of a hit and miss way of assessing intake of a vitamin and is open to biased interpretation. Vitamin K MK-4 is taken up rapidly by the brain, Vitamin K MK-7 found in hard cheeses and Natto products doesn’t cross the blood-brain barrier. So, other studies would need to follow it up with set dose supplemented vitamin K of the same type, to get a more reliable result.

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