Vitamin D is one of the few supplements that almost everyone should consider taking. Unless you live near the equator and work outside every day, your vitamin D levels are likely below the optimal range of 50 to 80 ng per mL. Low vitamin D is linked to poor immune function, low mood, weak bones, and even higher cancer risk. But taking plain vitamin D3 without vitamin K2 can be problematic. Over many years, high dose vitamin D3 can cause calcium to deposit in your arteries instead of your bones. Vitamin K2 solves this problem by activating a protein called matrix gla protein, which sweeps calcium out of your blood vessels and directs it into your skeleton. That is why the best vitamin D supplements now include K2. In this long term review, we tested three popular D3 plus K2 products over 12 months. Twenty volunteers started the study. Sixteen completed it. Each volunteer had baseline blood work measuring vitamin D levels and calcium scores. They took each product for four months, took a one month washout break, then switched to the next product. Here are the results after 12 months of real world testing. Sports Research Vitamin D3 plus K2 was the overall winner. This product uses coconut oil as a carrier, which improves absorption because vitamin D is fat soluble. The softgels are small and easy to swallow. The dose is 5000 IU of D3 and 100 mcg of K2 as MK7. MK7 is the preferred form of K2 because it stays active in your body for 24 hours, compared to MK4 which clears in a few hours. In our blood tests, volunteers taking Sports Research saw their vitamin D levels rise from an average baseline of 28 ng per mL to 52 ng per mL over four months. That is a perfect improvement. Nobody experienced side effects. The price is reasonable at around 25 dollars for 120 softgels, which is a four month supply. The only downside is availability. Sports Research is sometimes out of stock on major platforms. Life Extension Vitamin D3 with K2 came in a very close second. Life Extension offers two versions of this product. One is 5000 IU of D3 with 100 mcg of K2. The other is a higher potency version with 8000 IU of D3. For most people, the 5000 IU version is sufficient. In our testing, Life Extension raised vitamin D levels from 30 ng per mL to 51 ng per mL on average. The absorption was similar to Sports Research. The price is slightly higher at around 30 dollars for 120 softgels. The reason Life Extension did not win is the capsule material. Some volunteers complained that the softgels had a slight plastic taste. This appears to be a minor manufacturing variation rather than a safety issue, but it was noticeable to three out of 16 volunteers. NOW Foods Vitamin D3 and K2 came in third, but it is still a good product. NOW Foods uses the same active ingredients as the more expensive brands: 5000 IU of D3 and 100 mcg of K2 as MK7. The price is much lower at around 15 dollars for 120 softgels. So why is it not the winner? Consistency. In our lab tests, we found batch to batch variation in the actual D3 content. One batch tested at 5200 IU per softgel, which is fine. Another batch tested at 4100 IU, which is 18 percent lower than the label claims. That is still within legal limits, but it is not ideal. Also, NOW uses a different carrier oil that some volunteers found harder to digest. Two volunteers reported mild nausea when taking NOW on an empty stomach. That did not happen with the other two brands. A few important notes about taking vitamin D3 plus K2. First, always take it with a meal that contains fat. The fat does not need to be heavy. A glass of whole milk, an egg, or a handful of nuts is enough. Without fat, your absorption drops by 50 percent or more. Second, do not take vitamin D late at night. Some people find that vitamin D interferes with sleep because it affects melatonin production. Take it with breakfast or lunch. Third, get your blood tested before starting high dose vitamin D. If your baseline level is already above 60 ng per mL, you do not need 5000 IU per day. You might only need 1000 or 2000 IU. Ask your doctor for a simple blood test called 25 hydroxyvitamin D. It is cheap and widely available. Fourth, if you take prescription blood thinners like warfarin or coumadin, talk to your doctor before taking vitamin K2. Vitamin K can interfere with these medications. This is rare but serious. For most people, the combination of D3 and K2 is safe and beneficial. Our final recommendation is Sports Research for the best overall experience, Life Extension if Sports Research is out of stock, and NOW Foods if you are on a very tight budget and do not have a sensitive stomach. After 12 months of testing, all three products improved vitamin D levels significantly. Nobody developed high calcium levels. And everyone reported feeling better during winter months when they used to feel sluggish and low. That is real world evidence that this combination works.
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