Vitamin D3 and K2 for weight loss: Here's what science says

You know you need vitamin C for immune health, vitamin B for energy production, and vitamin A for supporting your vision.

But what about vitamin D3 and K2? You might not be as familiar with either, but you soon will be: this mighty combo is a favourite among health experts for helping your body absorb and use calcium properly — keeping your bones healthy, strong, and flexible. 

Aside from their benefits for your bone health, the pair may also support weight loss. Here's how.

What is vitamin D3?

First, let’s look at the perhaps more well-known vitamin of the two: vitamin D3.

Vitamin D is a necessary nutrient that supports bone and muscle health, the immune system, mood, brain function, and cardiovascular health. It also plays a role in metabolism and weight management, but more on that later.

When it comes to bone health, vitamin D is particularly essential because it helps your body absorb calcium, a building block of healthy bones.

A lack of calcium can lead to all sorts of bone problems, including a rather serious one known as osteoporosis — a condition that affects half of women aged 50+ and causes bones to become very brittle and fragile [1].

The two most common types of vitamin D are vitamin D2 and vitamin D3. The former is typically found in plant foods (like mushrooms) and the latter is found in animal sources (like egg yolks and fatty fish). 

Out of the two, vitamin D3 is the most effective form of vitamin D, meaning it’s generally better at boosting your body’s vitamin D stores.

Your body produces vitamin D3 when it’s exposed to sunlight, but for those who live in less-sunny countries (like the UK), it can be pretty tricky to get a sufficient amount.

That’s why there are loads of vitamin D supplements on the market. Vitamin D supplementation can be useful for raising your vitamin D levels if you're not making enough from sunlight

What is vitamin K2?

Now to the other half of the equation: vitamin K2.

This vitamin is also found in some animal products (think egg yolks and liver) as well as fermented foods (cheese, sauerkraut, kimchi, and a Japanese fermented soybean product known as natto).

Vitamin K2 is also crucial in calcium regulation. It works by activating a protein known as osteocalcin, which diverts calcium towards your bones and teeth, where it’s needed, and away from your arteries, where it's not. 

If too much calcium accumulates in your arteries and around your heart, it can lead to heart disease and arterial calcification (hardening of the arteries).

Like vitamin D, there are multiple types of vitamin K. Another is vitamin K1, found in leafy greens and primarily useful for blood clotting.

Vitamin K2 is generally considered the more potent of the two, as it’s more easily absorbed by the body and can stay in the body for longer — potentially prolonging its benefits.

How do vitamins D3 and K2 work together?

When the two vitamins are combined, they’re possibly even more impactful. In fact, some have dubbed the combo the ‘perfect pair’ thanks to their synergistic effects.

While vitamin D3 supports calcium absorption, K2 directs it to your bones and teeth and prevents it from building up in your arteries — making sure the calcium you absorb is spread to the right places and not to the wrong ones.

The result is stronger bones and improved heart health. 

In fact, a 2020 review showed that a mix of the two massively boosted bone mineral density (BMD) — a measure of bone strength — compared to intake via a normal diet or having no supplementation at all [2].

An earlier study also supports the benefits of taking both.

The study examined the impact of vitamin supplementation on postmenopausal women with osteoporosis, dividing the participants into 4 groups and supplementing them with calcium, vitamin D3, vitamin K2, or a combination of D3 and K2. 

Researchers concluded that pairing vitamins D3 and K2 had the biggest impact on BMD, producing a significant improvement [3].

How vitamins D3 and K2 impact weight loss

The perfect pair may also assist with losing weight. While neither supplement is a direct fat burner, several studies have shown that they can support weight loss indirectly.

As far as vitamin D3 goes, a couple of studies have demonstrated a positive influence on weight loss.

One study found that vitamin D3 supplementation resulted in a significant reduction in body fat compared to a placebo [4].

Another conducted on overweight and obese women concluded that while supplementation didn’t necessarily result in increased weight loss, those who ended up with adequate vitamin D3 levels lost more weight than those who didn’t [5].

Another still showed that vitamin D deficiency tends to be more common in obese people [6]. This may be because a lack of vitamin D is associated with poor fat storage and inflammation [7].

One reason why vitamin D may support weight loss is that it can boost the metabolism.

A study performed on mice found that a vitamin D-rich breakfast enhanced metabolism to burn fat and that vitamin D could protect against obesity by increasing fat cell death (which basically means that fat cells die off more easily) [8].

An additional reason is that vitamin D3 supports muscle growth, with evidence that it encourages protein synthesis, builds muscle tissue, and improves muscle size and strength [9].

Muscle mass is essential for weight loss because it burns more calories.

Vitamin D can also lower cholesterol, with a study in the American Journal of Clinical Nutrition finding that vitamin D and calcium supplementation led to a significant reduction in cholesterol levels [10].

High cholesterol is a common condition associated with being overweight or obese and increases the risk of cardiovascular issues. 

It could also be that because the combination of vitamins D3 and K2 helps deposit calcium in your bones, it supports your ability to exercise — possibly aiding your weight loss efforts. Physical activity is an essential component of weight loss, as it boosts metabolism, builds muscle, and burns calories. 

Evidence on the use of vitamin K2 on its own as a weight loss aid is still in its early stages, but there is some research demonstrating the vitamin’s potential. 

A 3-year study from 2017 found that a high intake of vitamin K2 can lower body weight, particularly visceral fat around the abdomen, which is considered the most dangerous type of fat [11].

Excess visceral fat is linked with an increased risk of heart disease, type 2 diabetes, and other serious health problems [12].

It is worth mentioning that no vitamin alone will necessarily result in weight loss.

Instead, weight loss is best treated with a holistic approach combining dietary changes, increased exercise and expert support. So while these vitamins may help, they shouldn’t be treated as a magic solution.

Top sources of vitamin D3 and vitamin K2

Given the health and possible weight loss benefits of both vitamins, you’re probably curious how you can get more of them. Fortunately, there are several ways to increase your intake.

(Wondering how much vitamin D and vitamin K you need? The NHS says that each day, adults require about 10 micrograms (mcg) of vitamin D and 1 mcg of vitamin K per kilogram of body weight [13][14]. If you weigh 70kg, for instance, you’d need around 70 mcg every day.)

Sunlight

Your body produces vitamin D when it’s exposed to the sun, which is why experts like to refer to it as the "sunshine vitamin".

Exposing your skin to the sun is also the easiest way to create vitamin D, depending on the time of year. 

According to the NHS, you can generally make enough vitamin D from sunlight from late March/early April to the end of September [13]. You only need to get about 10 minutes per day between 11 am and 3 pm [15]. Any more time than that and make sure to apply sunscreen!

From October to early March, it’s much harder to produce sufficient vitamin D. This is where dietary sources and supplements may come in handy.

Dietary sources of vitamin D3

You can get vitamin D3 from a bunch of different foods [13], including:

• Oily fish like salmon, sardines, and mackerel
• Red meat and liver
• Egg yolks
• Foods that have been fortified with vitamin D, like cereal, bread, and plant-based milk (note that cow’s milk isn’t fortified with vitamin D in the UK)

Dietary sources of vitamin K2

You’ll find vitamin K2 in a whole range of foods [16], such as:

• Fermented foods like sauerkraut, kimchi, kefir, natto, and cheese
• Chicken breast
• Egg yolks
• Chicken liver
• Butter

Experts warn that consuming excessive amounts of some K2-containing foods may be detrimental to your health [16].

Things like butter, chicken liver, and egg yolks should only be eaten in moderation, as an excess may lead to unhealthy cholesterol levels and too much saturated fat.

This is especially important if you’re watching your cholesterol or trying to lose weight.

Vitamin D and vitamin K supplements

There are lots of supplements on the market that contain vitamin D3, vitamin K2 or both. 

But remember, like any nutritional supplement, it’s absolutely possible to get too much.

Vitamin D toxicity, for example, can lead to a host of health issues including kidney problems and hypercalcemia (where there’s too much calcium in your blood) [17].

For that reason, it’s essential to chat with your healthcare provider and have your vitamin D and K levels checked before taking a supplement.

Relying on dietary intake and sunlight alone is unlikely to cause a dangerous excess because your body is able to naturally moderate its production [18].

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