Is vitamin D capitalized?

Is “Vitamin D” Capitalized? The Definitive Answer

​As you’ve probably noticed, sometimes researchers will capitalize substantives in papers – writing the first letter of ​a word in uppercase to give it focus.

​Have you ever wondered if this is grammatically correct? Given how many times I refer to vitamin D in my articles, I did.

​Let me share with you what I found out.


Is it correct to capitalize the word “vitamin”?

In English, you are expected to capitalize certain nouns, like proper nouns and adjectives derived from proper nouns, but not common nouns. (1)

The word “vitamin” is a common noun. Therefore, it shouldn’t be capitalized unless, for example, it’s part of a brand name or the first word in a sentence.


  • ​I ​like the supplements from Best Health Vitamin D.
  • ​Vitamin D is a wonderful molecule.
  • ​The Vitamin D Standardization Program was created by the NIH.


  • ​Don’t forget to take your Vitamin D.
  • ​I’m unsure if Vitamin D is as important as you think.
  • ​I really enjoyed attending the congress promoted by the vitamin D Standardization Program

What about the “D”?

Vitamins were named after letters. Letters are capitalized. So, it makes sense to capitalize them.

For example, suppose scientists decided to name these vital substances after famous writers instead. We’d have chemical compounds such as vitamin Shakespeare, vitamin Charles Dickens, and vitamin Jane Austen.

Proper nouns are capitalized, therefore, you’d never write “vitamin charles dickens.”

Accordingly, the Merriam-Webster dictionary, when referring to any of the vitamins, lists the word “vitamin” in lowercase but the accompanying letter in uppercase.

You can check some examples for yourself here:

However, if they had been named after everyday objects you wouldn’t have to worry about any capitalization.

You’d have vitamin table, vitamin chair, and vitamin chimney. Aren’t you glad I wasn’t the one naming vitamins?

If vitamins were named after everyday objects

Should you ever use a hyphen, as in “Vitamin-D”?

You may think the answer is “of course not.” But, as I’ve found out, the answer is not that linear.

As it turns out, in English, there’s at least one circumstance in which you must use a hyphen to connect the adjectives you are using to describe a noun: when these adjectives come before the noun they are describing. (2)


​Ingesting magnesium-rich food is good for you.

In this sentence, “food” is being described by the compound modifier “magnesium-rich.” The hyphen adds clarity to the message.

However, if these two words came after the noun there would be no need for the hyphen:

Ingesting food rich in magnesium is good for you.

In the same way, there’s a time and place for writing “vitamin-d.” For example, when referring to “vitamin-D-rich food”.

​Ingesting ​vitamin-D-rich food is good for you.

When all nouns are capitalized

When I studied German – just for fun, I didn’t actually learn to speak German beyond the basics – one of the first things I noticed was how word capitalization worked.

For example, look at this abstract (zusammenfassung) written in German:


​Vitamin D ist eine für den Menschen essenzielle Substanz, die eine zentrale Rolle bei der Regulation des Calcium- und Phosphathaushalts spielt, aber auch eine Reihe sogenannter nichtklassischer Wirkungen entfaltet wie immunmodulatorische Effekte, Steigerung der Insulinsekretion und Sensitivität sowie Einfluss auf Zelldifferenzierung und Apoptose. Als essenzielle Substanz muss Vitamin D dem Körper lebenslang in ausreichender Menge zur Verfügung gestellt werden.


Did you see anything out of the ordinary?

Let’s take a closer look:


Vitamin D ist eine für den Menschen essenzielle Substanz, die eine zentrale Rolle bei der Regulation des Calcium- und Phosphathaushalts spielt, aber auch eine Reihe sogenannter nichtklassischer Wirkungen entfaltet wie immunmodulatorische Effekte, Steigerung der Insulinsekretion und Sensitivität sowie Einfluss auf Zelldifferenzierung und Apoptose. Als essenzielle Substanz muss Vitamin D dem Körper lebenslang in ausreichender Menge zur Verfügung gestellt werden.


​Did you notice how many words are capitalized?

Most of them aren’t ​even at the beginning of a sentence. That’s how German works, all nouns are capitalized.

This might easily influence a translator to incorrectly capitalize a common noun, like the word "vitamin", when translating a paper from German to English.

Possible exceptions to these rules

Have you noticed how titles and subtitles sometimes capitalize every word?

This is called title case.

Here, at Vitamin D Answers, we use title case in both the titles of the articles and the subheadings.

However, as you’ve probably noticed, in our case, every word is capitalized.

That’s actually an improper use of title case.

At its purest form, title case is all about capitalizing the nouns, similar to how German works. This means the connecting words shouldn't start with an uppercase.

​Why capitalize every word, then?

When I post these articles, I select “title case” in the editor I use. This automatically capitalizes each word in the subheading. Maybe I should manually edit each subheading?

What do you think?

Be sure to let me know if you consider the proper use of title case as important as the correct capitalization of vitamin D.

How did I end up caring about the Proper capitalization of “vitamin D”?

I’m Portuguese, and, even though I’ve been learning English since I was 10 years old (I’m 31), I’m aware my English is still far from perfect.

When I wrote my book in Portuguese, I had to translate all the quotes from English to Portuguese. Translating from a second language into my mother tongue was a breeze. But, organizing my thoughts in a language foreign to me – English – and writing them down is much harder.

This problem is especially true because of my perfectionism. I’ll write, delete, rewrite and re-delete, multiple times, and I’ll still feel unsure if what I wrote sounds native-enough or not.

Microsoft Word’s grammar checker and a plug-in called Grammarly help, a lot, but in multiple occasions I find myself relying on a trick I learned years ago: I’ll grab a group of words and Google them in quotes. Then, I​'ll check if ​Google returns enough search results. I call it the "Native Index."

If ​a group of words has been written thousands of times before, I feel confident about using it.

This is most useful when I’m unsure about two variations of the same phrase.

For example, should I write “From Portuguese to English” or “From Portuguese into English”?

Let's check their respective Native Indexes:

Native index for "From Portuguese into English"

​"From Portuguese into English"

Native Index: 46,700

Native index for“From Portuguese to English”

​"From Portuguese to English"

Native Index: ​1,690,000

When both of my searches return thousands of results, I feel confident in using both variations. But, if one of the variations returns a lot of results (1.69 million) and the other ​a much inferior number (46,700), it’s easy to see which one I should choose: the one with the highest Native Index.

Because of this, translating my book from Portuguese to English was a long undertaking. (Can you guess why I chose “to English” instead of “into English”?)

For these reasons, you won’t imagine how happy I felt when I received an email from Henry Lahore, from, commending me, both on the contents of the book and on the quality of the English used in it. I felt ecstatic.

And there you have it.

Proper grammar is important for ​at least two reasons:

  • ​It allows ​you to communicate ​your thoughts ​in a pleasant way.
  • ​It gives credibility to what you say. After all, when a writer doesn’t ​care about his grammar, can ​you trust he cares about his research?

Unfortunately, as a side-effect, obsessing over grammar also makes me feel insecure about my writing and can be a true time waster. That’s not pleasant, at all.

If you have read this far, though, you are probably like me and have a great desire to improve the quality of your writing.

Tiago Henriques

With more than 10 years of experience as a Public Speaker, Tiago Henriques has done hundreds of public talks. He was born in 1987, in Portugal, and is the Author of 3 books — and counting — and the creator and editor of the Portuguese Science Project, "Ciência Desenhada," where complicated science is explained in a simple way, using whiteboard animation techniques. Tiago developed his own practical and down-to-earth teaching method inspired by his experiences with the Portuguese Deaf Community and their use of highly visual, descriptive and easy-to-understand language.

  • Bea baker says:

    So. The word if the word vitamin D comes in middle or end of sentence, use a lower case “v” for the word vitamin?

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