Fall Fatigue Isn't Laziness—Why Do You Lack Vitamin D Starting in October, and How Can You Fix It?

You know how it is. It gets dark earlier outside, it’s harder to get up in the morning, workouts feel like a struggle, and the first cold isn’t far off. You blame it on the weather, stress at work, or simply the fact that “that’s just how fall is.” But what if there’s a specific reason behind it—one that can be solved with a single small capsule, which you only take twice a week?

We’re talking about vitamin D. And also its lesser-known but no less important partner, vitamin K2.

Article contents:

• The Myth of the Summer Reserve: Why Summer Isn’t Enough
• The Shadow Rule: How to Tell When the Sun Is No Longer Working for You
• Vitamin D: The Silent Leader of Immunity, Muscles, and Bones
• Why Vitamin D Alone Isn’t Enough: The Secret of Vitamin K2
• MK7 vs. Regular K2: Why the Form Matters

The Myth of Summer Storage: Why Summer Isn’t Enough

It’s a tempting idea. Three months by the water, on a bike, or in the garden, and your body will build up reserves for the whole winter. The reality is more sobering. Although vitamin D is stored in adipose tissue, blood levels begin to gradually decline once summer ends. The body gradually “taps into” these reserves throughout the fall, and by the end of winter, a large proportion of us reach the threshold of deficiency—or fall below it.

You’re not alone in this. Estimates for Europe suggest that roughly one in three to one in two adults has insufficient vitamin D levels, and the situation is significantly worse in the winter months than in the summer.

The Shadow Rule: How to Tell When the Sun Is No Longer Working for You

Your skin can produce vitamin D on its own, but only when it’s exposed to enough UVB radiation. And that radiation only reaches the ground when the sun is high enough above the horizon. There’s a simple trick to tell: when your shadow is longer than you are, your skin produces virtually no vitamin D. Take a look at your shadow at noon in October. It’s really long. In the Czech Republic, this means in practice that from roughly October through March, natural vitamin D production is nearly zero. Neither a midday walk nor sitting by a window will help, because glass doesn’t let UVB radiation through. So for half the year, your body relies solely on what you provide through your diet and supplements.

Vitamin D: The Silent Master of Immunity, Muscles, and Bones

Vitamin D acts more like a hormone in the body. Receptors for it are found in almost every cell, which is why a deficiency manifests itself in many places at once:

• Immunity: Vitamin D contributes to the normal function of the immune system. And you need it most precisely during the time of year when everyone around you is coughing.
• Muscles and Strength: Vitamin D helps maintain normal muscle function. If you feel like your workouts aren’t going well in the winter, it might not just be the darkness.
• Bones and teeth: Without vitamin D, the body cannot properly absorb and utilize calcium from your diet. You can drink liters of milk, but your bones still won’t get what they need.

Who’s most at risk? People who commute to and from work in the dark. People over 40, because as we age, our skin produces vitamin D less efficiently. People with a higher body fat percentage, because adipose tissue “traps” it. And active athletes, whose bodies have higher demands for recovery and immunity.

Why Vitamin D Alone Isn’t Enough: The Secret of Vitamin K2

Here’s something most people don’t know. Vitamin D helps the body absorb calcium from food. But what happens to that calcium next? That’s where vitamin K2 comes in.

Think of it like a construction site. Vitamin D is the truck driver who delivers bricks (calcium) to the site. Vitamin K2 is the construction foreman who tells them exactly where to place them—namely, in the bones and teeth. Without the foreman, the bricks will just lie around where they don’t belong.

Vitamin K2 helps maintain normal bone health, which is why taking vitamins D3 and K2 together makes much more sense than taking them separately. That’s also why you’re seeing more and more combination supplements in stores. But not every combination is the same.

MK7 vs. Regular K2: Why the Form Matters

Vitamin K2 exists in several forms, and the most highly valued one is called MK7 (menaquinone-7). Its huge advantage is that it lasts significantly longer in the body than other forms. According to the manufacturer, MK7 has a half-life up to 48 times longer than that of common forms of vitamin K2. In practice, this means it “works” in the blood for a long time, so you don’t need to take it several times a day.

This is precisely the concept behind Prom-in Vitamin MK7+D3. Each capsule contains:

• 75 µg of vitamin D3 (cholecalciferol, the most bioavailable form of vitamin D)
• 150 µg of vitamin K2 exclusively in the form of MK7
• 300 mg of soy lecithin, which acts as a natural “carrier” and helps the body absorb both fat-soluble vitamins

And now for the best part. Thanks to its high potency and long-lasting effects, you only need to take one Prom-in MK7+D3 capsule every 3 days. No need to keep track of it every day—just take it twice a week with breakfast.

Which D3 + K2 to Choose: Two Options Based on Your Lifestyle

Want a proven staple at the best price?

Go for Prom-in Vitamin MK7+D3. Each capsule contains 75 µg of vitamin D3 and 150 µg of vitamin K2 in the MK7 form, supplemented with lecithin, which acts as a natural “carrier” and helps absorb both fat-soluble vitamins. According to the manufacturer, the MK7 form used has a half-life up to 48 times longer than that of standard forms of K2.

The best part is the dosage: 1 capsule once every 3 days. The package contains 60 capsules, so it will last you 180 days—exactly from October through March. At 139 Kč, that works out to less than one crown per day.

Do you work out, are you vegan, or do you want something extra for your body?

Then GymSupps Vitamin D3+K2 (MK-7) + Curcumin is the right choice for you. It combines vitamins D3 and K2 with a third ingredient that’s especially popular among active people: turmeric.

• Vitamin D3 from lichen —a vegan form, not from sheep’s wool (lanolin) as in most products
• Patented K2VITAL® (MK-7 all-trans) —a stable form of vitamin K2 in a substantial dose of 150 µg
• 280 mg of turmeric extract containing 95% curcumin, plus turmeric powder for the full spectrum of compounds
• Vegetable capsule, making it suitable for vegans and vegetarians

Curcumin is one of the most extensively studied plant compounds, and athletes often turn to it during periods of intense training. The recommended dosage is 1 capsule every other day, so a 100-capsule bottle will last up to 200 days—enough to cover the entire winter with some left over into spring.

Whichever you choose, the same rules apply:

• Always take it with a meal that contains fat. Vitamins D and K2 are fat-soluble. If you swallow the capsule on an empty stomach with just water, a large portion will pass through your body without being absorbed. The ideal choice is breakfast with eggs or plain yogurt, which will also provide you with calcium.
• Consistency is more important than a high dose. Set a reminder on your phone so you don’t forget.
• Do not exceed the recommended dosage. Vitamin D is stored in the body, so more does not automatically mean better.

Important note: If you’re taking blood-thinning medications (such as warfarin), consult your doctor before taking vitamin K2 or turmeric. Prom-in Vitamin MK7+D3 is not intended for children, pregnant women, or nursing mothers.

Don’t let winter sap your energy

Darkness and cold don’t have to mean half a year of fatigue, colds, and stagnation. All you need to do is realize that the sun won’t do the work for you starting in October, and give your body what it needs during this time of year. One D3 + K2 capsule a few times a week is perhaps the simplest health habit you can adopt this year.