Your genes determine your need for vitamin D during the winter period

- and throughout life

Your genes determine your need for vitamin D during the winter period Vitamin D is important for a strong immune defense, healthy bones and cardiovascular system, cancer prevention, and for the support of many other essential body functions. However, it is not enough to follow the official guidelines for intake levels or to rely on blood tests. According to Carsten Carlberg, a professor at the University of Eastern Finland (UEF), the explanation lies in the fact that we humans respond widely different to vitamin D, so the optimal vitamin D dose varies from one individual to another. Based on years of research, Carsten Carlberg therefore advises all adults living at northern latitudes to take 100 micrograms of vitamin D daily throughout the winter period, just to be safe. Earlier studies indicate that the official recommendations for vitamin D are based on a miscalculation that has had fatal consequences for public health.

When the sun sits in the sky during the summer period it is easy for us humans to synthesize vitamin D. This process is enabled by a chemical reaction between sunlight and a cholesterol precursor in our skin. First, we produce a hormone called cholecalciferol that is not biologically active. In the liver, cholecalciferol is converted into 25-hydroxyvitamin D by means of certain enzymes. This is the form of vitamin D that is measured in blood tests. When the body needs vitamin D, the kidneys convert 25-hydroxyvitamin D - or 25(OH)D – into the metabolically active form known as 1,25-dihydroxyvitamin D. This process requires the involvement of other enzymes.
Most cells in the body’s tissues have vitamin D receptors (VDR). Even though a blood sample indicated that the body’s need for vitamin D in the different tissues is covered, this is no guarantee, according to Carsten Carlberg, a professor in biochemistry at the University of Eastern Finland who has studied vitamin D and epigenetics for a considerable number of years.
It turns out that vitamin D controls around 5-10 percent of our genes by way of various on-off switches, which means that many cells are unable to function normally with too little vitamin D. This can have serious health consequences.

High, middle, or low vitamin D response?

Carsten Carlberg and his colleague Afrozul Haq are the authors of a review article in which they argue that Europeans differ widely when it comes to their ability to utilize vitamin D. Based on observations from two vitamin D studies, VitDmet and VitDbol, the two scientists conclude that study participants can be placed in one of three categories: High utilizers, middle-degree utilizers, and low utilizers. Interestingly, the participants’ blood levels of vitamin D did not necessarily correspond with their ability to utilize the nutrient. Twenty-five percent of the participants had poor utilization of vitamin D and therefore needed a larger dose in order to obtain the optimal health benefits.
Therefore, it is not enough to know how much vitamin D you have in your blood, because if the vitamin D is inactive, the cells are unable to benefit from it. According to the two scientists, it is the exact same thing you see when people respond entirely differently to the same medication.

Our genetic inheritance from the indigenous people of Africa and Europe

It is commonly known that people with dark skin synthesize vitamin D at a much slower rate than those with light skin. In the sunny regions from where these people originally came it is easy to produce sufficient amounts of vitamin D. Their dark skin served as a useful protection against sunburns. When some of the dark-skinned people headed towards northern latitudes thousands of years ago and were exposed to far less sun, they slowly developed lighter skin as a way of adapting to the scarce amount of UB radiation. Still, there are large variations.
In another review article, Carsten Carlberg and his colleague Andrea Hanel describe how the indigenous Europeans are descendants of the African hunters and gatherers, of the Anatolic farmers, and of the fair-skinned nomads from the Yamnaya plains in what is now Ukraine. All these populations have developed different abilities to synthesize vitamin D from sunlight and utilize it in their cells.

Blood samples don’t tell the whole truth about vitamin D utilization

According to Carsten Carlberg, you have to study a person’s cells in order to determine how well he or she responds to vitamin D. Theoretically, a person with insufficient vitamin D levels in the blood may respond equally well to vitamin D as someone with high blood levels of the nutrient. This also means that a person who responds well to vitamin D may get through the entire winter period without contracting any infections or experiencing deficiency problems. A high-responder may therefore be able to maintain the normal physiological functions of vitamin D without taking a supplement.
However, people who are low-responders may risk getting virus infections and other signs of deficiency, even though their blood levels of vitamin D are sufficient. It should also be mentioned that we need magnesium to support various enzymes that are used to activate vitamin D.

How much vitamin D do we need?

The reference intake (RI) level for vitamin D (in Denmark) is five micrograms for white adults under the age of 70, while the Danish Health Authority recommends a daily 10-microgram supplement for pregnant women, infants, dark-skinned people, and individuals that get too little sunlight. Nursing home residents and people older than 70 are advised to take 20 micrograms of vitamin D daily.
In Finland, the official recommendation for vitamin D is 20 micrograms per day. However, according to Carsten Carlberg, some people may need more. A person that responds well to vitamin D may be able to get by with 25 micrograms daily, while a low-responder may need around 100 micrograms. The ideal thing to do is to have your vitamin D response measured at least once in your lifetime to make sure that you get enough on a daily basis
In order to simplify matters, Professor Carlberg advises Fins and other people living at northern latitudes to take a 100-microgram vitamin D supplement every day during the winter period. Those who respond well to vitamin D may actually be getting more than they need, but it is perfectly safe and ensures that people who are not good responders get enough. Although 100 micrograms per day is way above the official recommendation, it is not more than the amount that we can synthesize on a warm summer day.

Official recommendations are based on a serious miscalculation

Professor Cedric Garland, an American scientist from the University of California has been one of the leading vitamin D researchers for decades. In collaboration with some colleagues, Garland has written an article in the science journal Nutrients, in which he explains why the official vitamin D recommendations are way too low. The scientists claim it is based on a miscalculation. The official recommendations are not designed to ensure optimal blood levels of the nutrients. This would require 75-175 micrograms from a variety of different vitamin D sources, including the sun. According to Cedric Garland and his colleagues, this miscalculation has had fatal consequences for public health, and they urge the health authorities to take action.
With regard to supplements, the European Food Safety Authority (EFSA) has set the safe upper intake level at 100 micrograms per day, which is exactly the same amount as Carsten Carlberg recommends.
Although experts disagree widely when it comes to people’s actual need for vitamin D, it is essential under all circumstances to make sure to get plenty of sunlight during the summer and to take a high-dosed vitamin D supplement during the winter period. It is also important that the vitamin D in the supplement is dissolved in oil in gelatin capsules for optimal bioavailability.

Blood levels of vitamin D are normal categorized as deficiency (below 30 nmol/L), insufficiency (30-50 nmol/L), and sufficiency (above 50 nmol/L).

According to several scientists, the optimal level for vitamin D is between 60-100 nmol/l.

Levels higher than 125 ng/mL (312,5 nmol/l) may cause side effects such as nausea, constipation, weight loss, heart rhythm disturbances, and kidney damage.

The ability to utilize vitamin D depends on magnesium and our genes


Helene Sandström. Den optimala D-vitamindosen i vinter? Det beror på dina genar. Nordic Nutrition Council. Sep. 3 2020 Interview mit Dr. Carlberg: Vitamin D, epigenetik und der respons-index. Hämtad. 2020-09-03

University of Eastern Finland. Vitamin D and skin color revisited – student exchange opens doors to research. Pressmeddelande. 2019

Carsten Carlberg, Afrozul Haq. The concept of the personal vitamin D response index. The Journal of steroid biochemistry and molecular biology. 2016

Andrea Rosanoff et al. Essential Nutrient Interactions: Does Low or Suboptimal Magnesium Interact with Vitamin D and/or Calcium status. Advances in Nutrition 2016

Robert Heaney, Cedric Garland and Edward Gorham: A Statistical Error in the Estimation of the Recommended Dietary Allowance for Vitamin D. J. Nutrients. 2014

Cedric F Garland et al. Vitamin D Supplement Doses and serum 25-Hydroxyvitamin D in the Range Associated with Cancer prevention. Anticancer research 2011

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