How to Eat Smart in Winter | You May Be Lacking Vitamin D

Honest people don't speak in secret.

As a registered dietitian whose aim is to provide "balanced and reasonable diet", and as a master of Chinese medicine diet therapy who believes that "food supplements are worse than medicine supplements".

Today, I want to tell you straight out of the box: remember to take vitamin D in winter!

Why do we need to make up for it? Because we lack it!

Unlike most nutrients that can be met by food intake, most of the vitamin D in the human body is synthesized through skin exposure to ultraviolet light (UVB) at 290–315 nm, and only a small part comes from daily dietary intake of vitamin D.

Complex factors including latitude, UV intensity, sunshine time, skin color, skin exposure area, season, and air pollution can affect skin vitamin D synthesis.

Most of my country is located in the mid-latitudes of the northern hemisphere, with four distinct seasons. In autumn and winter, the sunshine angle is low, the duration is short, and the haze is heavy. In addition, when going out, wrapping yourself up tightly, with only your eyes exposed except for the mask, will seriously affect the synthesis of vitamin D and directly lead to vitamin D deficiency.

Vitamin D deficiency is a global public health problem in modern society, not just in China.

How many people are deficient in vitamin D? Let’s first look at South Korea, which is also located in the mid-latitudes of the Northern Hemisphere.

The Department of Pediatrics at Korea University Hospital in Seoul analyzed the serum 25-(OH)D levels of Korean children under 10 years old on a monthly basis:

Serum vitamin D levels were divided into three categories: adequate (≥30 ng/mL), insufficient (20-30 ng/mL), and deficient (<20 ng/mL).

The result shows 1:

●For children who received vitamin D supplementation, the average vitamin D level was 30.59 ng/mL, while that of the non-supplemented group was 22.33 ng/mL.

●During the year, 58.1%, 32.1% and 35.8% of the children in the supplemented group were in the appropriate, inadequate and deficient groups, respectively; and 41.9%, 67.9% and 79.4% of the children in the non-supplemented group were in the different statuses (due to different monthly vitamin D levels, the same child may be in different statuses within a year).

●There was no significant difference in vitamin D levels in each month in the supplemented group; the vitamin D level in the non-supplemented group was lowest in March (17.2 ng/mL) and relatively highest in August-September (30.5 ng/mL).

* Vitamin D nutritional status of Korean children by month and whether or not they took vitamin D supplements

You may think: Korea is at a higher latitude! I live in Central China, South China, and even Hainan, so it is impossible for me to be deficient in vitamin D!

Now, let’s take a look at the National Nutrition Monitoring Data (CNNS) released by the Chinese Center for Disease Control and Prevention in 20212.

The results showed that even in tropical areas such as Guangzhou, Shenzhen, Haikou and Sanya, the rate of vitamin D deficiency among pregnant women was still as high as 58.7%; in the "southern region" south of Qinhuai River, the deficiency rate was 82.3%; and in the north, as many as 95% of pregnant women were in a state of vitamin D deficiency.

What's worse is that by comparing the national nutrition monitoring data from 2015-2017 and 2010-2012, we can find that the vitamin D deficiency rate among Chinese pregnant women is on the rise! It is reasonable to guess that this is because pregnant women have less outdoor activities, do not do a good job of sun protection, and do not eat enough vitamin D, which leads to the fact that most pregnant women and fetuses are at risk of vitamin D deficiency.

Pregnant women are the group of adults who pay the most attention to nutrient supplementation. If they are like this, what about others?

*Proportion of vitamin D deficiency among pregnant women in China by latitude

What will happen if you don’t make up for it? There are a lot of risks!

According to nutrition textbooks, the typical symptom of vitamin D deficiency is that it affects bone metabolism, leading to bone diseases such as rickets in infants and young children, osteomalacia in pregnant women, and osteoporosis in middle-aged and elderly people.

Do you think it is still far away from you? No!

The absence of typical symptoms does not guarantee that serum vitamin D levels meet the standard. Adequate vitamin D levels are beneficial for chronic disease management and reduce the risk of cardiovascular death, diabetes, allergies, asthma, kidney disease and other diseases1. Chronic vitamin D deficiency without symptoms may lead to a series of "sub-health" conditions such as fatigue, depression, muscle pain, back pain, etc.1.

Today, in the new normal of the global epidemic, the relationship between vitamin D nutritional status and infectious diseases has received unprecedented attention from the medical community.

Since 2020, scholars around the world have published nearly a thousand papers, exploring hot topics including:

●The correlation between reduced outdoor activities during the epidemic and vitamin D deficiency.

●The correlation between vitamin D nutritional status and the risk of COVID-19 infection, severity of the disease, and antibody production rate after vaccination.

●Can vitamin D supplementation reduce complications, improve clinical outcomes, and achieve better recovery from COVID-19?

*Total number of articles retrieved from Pubmed using the keywords vitamin D and Covid-19

How much? 400-1000 IU! The U.S. Dietary Guidelines 2020-2025 recommend that all infants should begin taking vitamin D supplements as soon as possible after birth.

The Chinese Dietary Guidelines recommend that infants start taking vitamin D supplements a few days after birth; except for people over 65 years old, who are recommended to take 600 IU/day of vitamin D, all other groups should take 400 IU/day. The UK currently recommends 400 IU/day, while the EU recommends 600 IU/day.

In special circumstances, the recommended vitamin D intake may need to be further increased.

At the end of 2020, several scholars from the University of London, the University of Liverpool and the University of Birmingham wrote an article pointing out3:

"The current serum vitamin D value set by the UK is low (about 10ng/mL) and should be increased to at least 20ng/mL. Supplementing 800IU of vitamin D per day is safe and effective in improving serum vitamin D levels. Daily intake of vitamin D within 4000IU is generally recognized as a safe dose*. It is recommended that all adults supplement 800-1000IU of vitamin D per day. During the COVID19 pandemic, this measure should be urgently promoted in the UK."

"It is cheap and convenient to get vitamin D through dietary supplements. We have nothing to lose and a lot to gain."

*Note: The maximum tolerable intake recommended by the Chinese Nutrition Society is 2000IU.

Finally, I emphasize again:

Friends in my circle of friends who are good at maintaining their health, in addition to protecting their hair, will also pay attention to maintaining a good level of vitamin D.

After all, if you lose your hair, you can wear a wig, and if your skin has dark spots, you can beautify it with one click using photo-editing software.

But if you have a cold, a fever, muscle aches and general weakness, you can only watch your friends go out and have fun on WeChat Moments...

References

[1]. Won JW. Seasonal Changes in Vitamin D Levels of Healthy Children in Mid-Latitude, Asian Urban Area. Pediatr Gastroenterol Hepatol Nutr. 2021 Mar;24(2):207-217.

[2]. Hu Y. Vitamin D Nutritional Status of Chinese Pregnant Women, Comparing the Chinese National Nutrition Surveillance (CNHS) 2015-2017 with CNHS 2010-2012. Nutrients. 2021 Jun 29;13(7):2237.

[3]. Griffin G. Preventing vitamin D deficiency during the COVID-19 pandemic: UK definitions of vitamin D sufficiency and recommended supplement dose are set too low. Clin Med (Lond). 2021 Jan;21(1):e48-e51.

Author: Liu Youjiao | Registered nutritionist and popularizer of Chinese nutrition knowledge

Reviewer Xu Shufang | Chief Physician of Clinical Nutrition Department

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