It was pretty eye-opening (and alarming) when I read it.
In short: While Vitamin D is great for everyone, your body will begin lacking in vitamins A and K because of the effects of D (too much of a good thing, essentially). It's all about finding the right balance for yourself.
Snippet from the closing:
1. Get enough vitamin D… but not too much. Doses of around 1,000 IUs per day — even as high as 2,000 IUs a day in the winter months when you’re not exposed to much sunlight — are likely safe. Especially when other key nutrients are included, such as vitamin K, vitamin A, and magnesium. You can ensure you are getting enough of these by taking a quality multi-vitamin.
2. Support vitamin D’s work Remember that other nutrients act together with vitamin D. Consume a wide variety of minimally processed foods to help get vitamin D’s nutritional colleagues such as magnesium, vitamin A, and vitamin K.
Eat your greens and fermented foods. Dark leafy greens — such as kale, spinach, or Swiss chard — are good sources of vitamin K1. They’re also high in dietary magnesium. Fermented veggies such as sauerkraut along with eggs, meats (especially organ meats such as liver) and fermented/aged cheeses are good sources of vitamin K2.
Eat the rainbow. The carotenoid form of vitamin A is found in colorful fruits and veggies. Eggs, butter, full-fat dairy (such as cheese) and organ meats are also great sources of the active retinol form of vitamin A.
Keep your intestinal flora happy and healthy. Vitamin K conversion happens in the GI tract. So eat plenty of fermented foods and prebiotic fiber, consider a probiotic supplement, and avoid antibiotics unless absolutely necessary (research has found that broad-spectrum antibiotics can reduce K production by up to 75%).
Review all medications and supplements with your doctor and/or pharmacist. Many medications, such as corticosteroids like Prednisone, weight loss drugs like Orlistat, cholesterol-blocking drugs like statins, and/or high blood pressure drugs like thiazide diuretics can disrupt the delicate balance of vitamin and mineral regulation in the body. Make sure you know all the side effects and interactions of any medications (or “healthy” supplements) you are taking.