Why do vitamin D levels go down so easily?

why do vitamin D levels go down

Worldwide, there is a problem that is often neglected or ignored by health authorities: vitamin D deficiency. At least 50% of the elderly population of all Europe and North America, both men and women, have low plasma levels of vitamin D.

I was born in Italy, where the sun shines for most days of the year. Curiously though, Italy is one of the countries with a prevalence in subjects deficient in vitamin D among the highest in Europe. This high prevalence creates a very worrying scenario, where 82% of vitamin D deficiency is found in people over the age of seventy during winter months. The percentages are higher in older people, but this nutritional lack is also common in young people and premenopausal women, with a marked increase in the case of obesity.

These percentages are incredibly worrying, and decreasing vitamin D blood levels are a problem in many countries worldwide.

To be able to solve a problem, it is first necessary to understand it well; therefore, let me spend a few words to introduce vitamin D and all the benefits that it brings to the body.

What is vitamin D?

why do vitamin D levels go down

Vitamin D is an essential nutrient for the human organism. It is not only responsible for the regulation of skeletal homeostasis, but it also has many other benefits thanks to the fact that its receptor is present in many organs and tissues. Many studies have shown the benefits of taking enough vitamin D for various extra skeletal conditions, such as in the prevention of neoplastic, autoimmune, and cardiovascular diseases. Vitamin D is essential to help the body absorb a range of nutrients such as calcium, magnesium, and phosphate.

Vitamin D exists primarily in two forms: vitamin D2 and vitamin D3, the latter generated through chemical reactions that occur when human skin meets sunlight. It is also possible to take vitamin D (indeed, I recommend you do it in cases of insufficiency) also through food or supplements. I will shortly explain which are the doses recommended by nutritionists.

But what are the health benefits of vitamin D?

  • Vitamin D is a must for the health of the skeleton; it keeps bones strong and healthy for a long time and helps their development. It is essential for children and young people of developing age, but also for the elderly, to protect their bones from the risk of osteoporosis.
  • It significantly improves the functioning of the immune system.
  • It contributes to muscle tone and physical strength.
  • It significantly improves skin health, although several precautions are needed to reduce the risks of sun exposure.
  • It improves mood.

Vitamin D is a valuable ally of your health, and addressing its deficiency helps prevent all the consequences on health.

Which foods contain vitamin D?

food rich in vitamin D

Curiously, vitamin D is naturally produced by our metabolism in an inactive form, which is activated under the skin when exposed to sunlight. If you cannot expose yourself to the sun (due to hypersensitivity to sunlight or as it happens during wintertime), you should know that some foods contain this vitamin. Here are the main foods that contain vitamin D:

  • Cod liver oil.
  • Fresh salmon (both caught and bred).
  • Canned fish (salmon, tuna, mackerel, sardines).
  • Fresh or smoked Shiitake mushrooms.
  • Egg yolk.

These are the foods that contain vitamin D. However, some other foods, although they do not contain this vitamin naturally, are fortified with vitamin D during their production. These foods can significantly contribute to vitamin D intakes.

Here they are:

  • Fortified milk.
  • Fortified orange juice.
  • Preparations for baby food fortified.
  • Fortified yogurt.
  • Fortified butter.
  • Fortified cheeses.
  • Fortified breakfast cereals.
  • Energy bars (check the label to see if they contain vitamin D).
  • Replacement meals (check the label to see if they contain vitamin D).
  • Protein drinks (check the label to see if they contain vitamin D).
  • Fortified soy drinks.

In these foods that naturally do not contain vitamin D, the manufacturer has added it during the production process. It is always best to check the label to verify that the purchased product contains vitamin D.

However, care is needed when cooking foods that contain vitamin D. Although the latter is less sensitive to cooking compared to other vitamins, some cooked foods may have lost part of their vitamin D content. However, the loss is still often small, and therefore the intake of vitamin D does not decrease excessively.

Differences between vitamin D2 and D3

Shiitake mushrooms

There are several types of vitamin D; the most common ones are vitamin D2 and D3.

What makes them different?

Vitamin D2 is synthesized by plants (for example, in sun-dried mushrooms, and in some types of mushrooms that are irradiated by UV rays to increase their production of this vitamin), and it is present in some supplements for vegetarians and vegans. Vitamin D3 is instead activated under the skin during sun exposure (it is also called the sun vitamin), and most traditional supplements contain it. There are no proofs that demonstrate that vitamin D3 is more effective than D2, although several laboratory tests seem to support this thesis. However, both vitamins excellently perform their work, and D2 is also suitable for those who follow a vegan diet. Plasma vitamin D levels measured with the 25OHD parameter detect both isoforms. Vitamin D2 has a shorter half-life than D3, and this has raised doubts about the possibility that vitamin D2 is less active than D3. The different half-life is simply because vitamin D3 is bound to a cofactor that makes it more stable over time, even if it may reduce its effectiveness. Vitamin D2 has the same functions as D3, and, in general, there are currently no reasons to think that it can have, for example, a minor effect on fracture prevention.

How are lack, deficiency, and excess of vitamin D defined?

why do vitamin D levels go down

To measure vitamin D levels in your blood, you just need to do a simple laboratory analysis on your blood through a routine test that measures the levels of vitamin 24OHD.

These are the values ​​that science holds to compare whether the levels of vitamin D in the blood are sufficient or not:

Deficiency: < 50 nmol/l or <20 ng/l

Insufficiency: Between 50 and 75 nmol/l or between 20 and 30 ng/l

Excess: > 250 nmol/l or > 100 ng/l

Intoxication: > 375 nmol/l or > 150 ng/l

What do doctors mean by deficiency or insufficiency?

They mean that the amount of vitamin D present in the blood is below the minimum recommended levels and that this condition can generate a series of health problems if neglected.

Symptoms that suggest vitamin D deficiency or insufficiency are:

  • Chronic muscle pain.
  • Chronic fatigue.
  • Young children might start to walk later compared to other children.

Although these symptoms do not appear in all cases of deficiency, they are so generic that they can be mistaken for many other health conditions. In the upcoming sections, I will explain who is at risk and which consequences a vitamin D deficiency has on health.

Vitamin D deficiency or insufficiency is a big problem, but too much vitamin D is also a problem. These are the consequences of excess or intoxication with vitamin D:

  • A feeling of sickness.
  • Vomiting.
  • A significant drop in appetite.
  • Sense of constipation.
  • General weakness and feeling of chronic fatigue.
  • Itch.
  • Feeling of constant thirst and dehydration, which leads to drinking very often.
  • You urinate much more often.
  • A general feeling of confusion, particularly common among the elderly.
  • An increased heart rate.
  • Kidney problems.
  • Rapid weight loss.

Taking too much vitamin D is a severe mistake because our body can only use part of it for various chemical processes in the body. Vitamin D intoxication is also a severe problem that can lead to the health problems mentioned above, although they can be confused with the symptoms of other health conditions. Some studies have shown that taking too much vitamin D does not bring any benefits to bones (which was believed, by mistake until a few years ago), but it even worsens the situation.

However, these findings do not apply to those who take vitamin D under medical supervision since your doctor will have to be able to calibrate the dosage of vitamin D in a way that there is no risk of an overdose.

The intake of vitamin D supplements must take place under the supervision of the doctor or nutritionist in order not to risk an overdose.


Why does vitamin D plasma levels decrease?

vitamin D supplements

Vitamin D is present in an inactive form subcutaneously, and it is activated by specific chemical reactions that take place on contact between sunlight and the skin. It would seem simple: spend a lovely day at the beach or in the mountains on a sunny day, sunbathe all day and come back with a significant vitamin D dose.

It seems easy, maybe too easy, and it isn’t. It is never advisable to stay in the sun without protection, and there are conditions to be respected in order not to burn yourself or risk your health. Furthermore, several factors can cause a lack of absorption of vitamin D, still causing a deficiency.

But what are these cases? There are surprising ones:

  • Inadequate exposure to sunlight. It occurs mainly in the winter period.
  • During sun exposure, especially in the hottest hours of the day, it is always advisable to apply sunscreen. Still, research has shown that using a sunscreen with protection 30 or higher on the skin significantly reduces the absorption of vitamin D, even up to 95%.
  • The color of your skin. People with dark or olive skin have more natural protection against the sun’s rays than those with fair skin or those with freckles and susceptible skin (it is a sort of natural sunscreen). However, to reach the same levels of vitamin D as a person with fair skin, they need 3-5 times longer exposures.
  • A variety of diseases, such as liver disease or kidney disease, can prevent the conversion of vitamin D from the biologically inactive to the active form.
  • Use of drugs that interfere with the metabolism of vitamin D, such as anti-rejection drugs, anti-seizure drugs, antiviral drugs, or also medicines to control HIV.
  • People who live far from the equator can have a deficiency of vitamin D, especially in countries where the winter months have very little light.
  • Perform too little physical activity in the open air.
  • Above-average requirements for vitamin D.

There are also many risk factors which, although they are not the leading causes of vitamin D deficiency, can represent a risk factor.

Here are the main ones:

  • Cigarette smoke (it alters the metabolism of vitamin D).
  • Age. Older people’s skin has lost some of its ability to produce active vitamin D.
  • Obesity. Adipose tissue interferes with the production of vitamin D.
  • Alcohol abuse, which damages the intestinal absorption of vitamin D.
  • Osteoporosis.
  • Prolonged breastfeeding (which is a problem for the newborn).
  • Celiac disease.
  • Presence of a gastric bypass.
  • Lymphoma.
  • Kidney problems.
  • Chronic pancreatitis.

Individuals at risk of vitamin D deficiency

Vitamin D deficiency

As we have seen, vitamin D deficiency is a problem that affects many people all over the world and of all ages. Still, it is crucial to understand which individuals are most at risk to better target care and to develop a better awareness of the problem and of the preventive measures that can be put in place to prevent it.

What are the categories of people who are most at risk for vitamin D deficiency? Here they are:

  • Babies who were breastfed for too long time.
  • Senior people with stories of shoulder falls or stories of non-traumatic shoulder fractures.
  • People with dark skin who, as already written, naturally limits the absorption of vitamin D, mainly of African American and Hispanic ethnicity.
  • People with various diseases, such as celiac disease or liver disease.
  • Obese people.
  • People who have a gastric bypass.
  • People addicted to alcohol.
  • Smokers.
  • People who have contracted HIV.
  • Pregnant and lactating women.
  • People who don’t leave their homes often.

These are the main categories at risk and which, for one reason or another, are unable to take or produce enough vitamin D for their body.

The consequences of vitamin D deficiency

why do vitamin D levels go down

But what exactly are the consequences of a vitamin D deficiency?

Several consequences can arise due to the lack of vitamin D, and research is still ongoing to find them all. Not all the scientific world agrees in stating that there is specific evidence for some of these symptoms. However, these are the main ones:

  • Pain in bones and joints.
  • A general muscle weakness.
  • Weak bones that tend to deform in younger subjects and easily break in the elderly.
  • Depression.
  • High sweat in the head and hands.
  • Cramps and spasms.
  • There is an association between vitamin D deficiency and a range of cancers, such as pancreatic, colon, breast, and prostate cancer.
  • Cardiovascular disease, although in this case, the scientific literature is not flatly consistent.
  • Problems during pregnancy, including C-section and the occurrence of caries.

In the USA, about 50% of children aged 1 to 5 years old and 70% of those between 6 and 11 years suffer from vitamin D deficiency, with significant consequences on their physical development. This phenomenon occurs despite the presence on the market of many foods artificially enriched with vitamin D, such as milk or fruit juices. Scientists identify as causes of this problem a substantial drop in milk consumption (replaced by other breakfast drinks), the use of too strong sunscreens, and the more prevalent unhealthy eating habits among children.

Overall, 30% of children and 60% of the world’s adult population suffer from vitamin D deficiencies.

How to treat vitamin D with supplements according to age group

You can supplement the daily vitamin D dose through foods that contain it (see above) or through supplements. Regarding the latter, it is advisable never to take personal initiatives and consult a doctor or a nutritionist, since the excess and, especially, the intoxication by vitamin D have more negative effects than its deficiency.

Your doctor or nutritionist will help you decide the correct dosages of vitamin D based on your plasma levels, your sex, and age. These are the general guidelines for the recommended values ​​of vitamin D by age group. Each international unit (IU) corresponds to 25 ng of vitamin D.

  • Children up to one year of age: 400 IU/day.
  • Children from one year of age: 600 IU/day to maximize bone health.
  • Adults from 19 to 50 years: 600 IU/day.
  • Adults between 50 and 70 years: 600 IU/day.
  • Adult from 70 years: 800 IU/day.
  • Pregnant and lactating women: 600 IU/day.
  • Obese children and adults, people who take anti-seizure or AIDS medications. These people should get three times the recommended value of Vitamin D for their age group.

These recommended values ​​ only represent a general reference. Depending on the values ​​detected by the blood tests, your doctor or nutritionist may decide to recommend a higher or smaller daily dosage of supplements.

Vitamin D intoxication

why do vitamin D levels go down

I must say that it is practically impossible to become intoxicated with the vitamin D present in the sun’s rays because sun rays will destroy the excess vitamin D.

The intoxication problem arises from the wrong use of supplements or prescription errors, and it occurs when taking too high quantities of supplements for an extended time.

Another cause of intoxication is the accidental confusion in the dosages during the production of a supplement. For example, micrograms and milligrams can be confused, resulting in a 1000-fold higher dose of vitamin D in a supplement. The consumer, unaware of this error, carefully follows the medical indications but takes much more vitamin D and, in the long run, intoxication symptoms arise.

Recommendations for sun exposure

Being outdoors is a great cure-all for health and is the best way to fill up on vitamin D, but some recommendations are necessary. Here they are:

·       The skin can activate only little vitamin D before 9 am and after 3 pm due to the angle of sun rays.

·       Depending on your skin type, it may be necessary to prolong exposure to the sun to produce vitamin D, even if you have fair skin. Consult your doctor or dermatologist for information on safe sun exposure.

·       A sunscreen with a protection of 30 absorbs 97.5% of the solar radiation and reduces the production of active subcutaneous vitamin D by 97.5%. It is possible to expose yourself for 15 minutes a day without protection, in the less hot areas of the day.

·       Be careful of the clothes you wear, as they also shield the sun’s rays. Better to use light-colored clothes that are not too heavy.

Vitamin D deficiency: conclusions

After reading this post, it will seem clear to you the significant contribution that vitamin D brings to our health and how its deficiency is a big problem. It is useful to spend time outdoors and eat foods that contain this vitamin, as well as consult a doctor regarding the intake of supplements. Share with others the knowledge of all the beneficial effects of vitamin D and contact me if you have any questions.

Picture of Gianluca Tognon

Gianluca Tognon

Gianluca Tognon is an Italian nutrition coach, speaker, entrepreneur and associate professor at the University of Gothenburg. He started his career as a biologist and spent 15 years working both in Italy and then in Sweden. He has been involved in several EU research projects and has extensively worked and published on the association between diet, longevity and cardiovascular risk across the lifespan, also studying potential interactions between diet and genes. His work about the Mediterranean diet in Sweden has been cited by many newspapers worldwide including the Washington Post and The Telegraph among others. As a speaker, he has been invited by Harvard University and the Italian multi-national food company Barilla.

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