Vitamin D intake - also in summer???

18.06.21

Dr. Wolfgang Schachinger

Vitamin D intake - also in summer???

"I have now stopped taking my vitamin D drops/capsules because it is summer and the sun is shining outside."

Is this right?

There are many myths and opinions about taking vitamin D. It is also claimed by officials and by many doctors that supplementation of vitamin D is unnecessary in the summer months, as sufficient of it is produced in the body by spending time outdoors. Is this opinion in line with the current state of science?

Almost all body cells have vitamin D receptors that ensure that vitamin D can enter the cells and dock with the cell nucleus. There, vitamin D can activate about 2000 of 23000 genes, i.e. almost 10% of all genes.

Endogenous vitamin D synthesis

Vitamin D can only be produced in the body when UV-B rich sunlight hits the skin and triggers the production of vitamin D from cholesterol. We only get this UV-B-rich sunlight between 11 a.m. and 3 p.m. , and only from April to the beginning of September. Only by exposing a large part of the body surface to direct sunlight for about 20 minutes during this time can you produce exactly the amount of free vitamin D your body needs. Ask yourself: How many days a year are you in the sun between 11 am and 3 pm? For most people this is only the case on holiday, and even then many people avoid the midday sun.

Avoid sunburn

Although direct exposure to the sun at midday is the only way to produce vitamin D on your own, it is essential to manage your sun exposure to avoid sunburn. This means that you should arrange your stay in the sun in such a way that you expose a large part of the body surface unprotected to the sun for about 15 minutes. Depending on your skin sensitivity, you should either cover a large part of the body surface with clothing or apply a sunscreen 10 - 20 minutes after you start sunbathing. If you apply sunscreen at the beginning of sunbathing, you will prevent the body's own production of vitamin D. This also applies to children! This also applies to children! Vitamin D is also not formed indoors! This is why the following also applies on sunny days in summer: as long as you are indoors or outdoors with your clothes on, the body CANNOT produce vitamin D. This is why even on days like these, the body's own vitamin D production does not take place. That is why a vitamin D intake is also recommended on days like these.

Difference daily/weekly/monthly intake

New studies by Prof. Dr. Hollis and his working group of top experts in vitamin D have shown that there is a big difference in effect between free and bound vitamin D. Put simply, vitamin D is only available in the body as "free" vitamin D in the first few hours after ingestion. After that, it is bound to transport proteins. This bound vitamin D can no longer achieve many important metabolic effects. Only if vitamin D is taken in the recommended dose of about 1000 international units per 20kg body weight daily, sufficient free vitamin D circulates and is thus available to all body cells to prevent disease processes. Based on this study, daily intake of vitamin D is clearly more effective than administration of vitamin D at intervals of weeks or months.

Summary

The sun vitamin D can only be produced by the body itself if there is direct sun exposure for 10 - 20 minutes between 11 am and 3 pm on summer days. For longer sun exposure, appropriate protection against sunburn should be provided by clothing or sunscreen. New studies show that vitamin D is bound to transport proteins in the body within a short time. Only free, unbound vitamin D can unfold all the valuable effects of vitamin D for health. Therefore, daily intake of vitamin D is preferable to high-dose therapy with weekly or monthly intake intervals.

Sources:

  1. DeLuca HF, Darwish HM, Ross TK, Moss VE. Mechanism of action of 1,25-dihydroxyvitamin D on target gene expression. Journal of nutritional science and vitaminology 1992;19-26
  1. Hollis, B. W., & Wagner, C. L. (2013). The Role of the Parent Compound Vitamin D with Respect to Metabolism and Function: Why Clinical Dose Intervals Can Affect Clinical Outcomes. The Journal of Clinical Endocrinology & Metabolism, 98(12), 4619-4628. doi:10.1210/jc.2013-2653.

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