Lekarz mówi, że potrzebuję więcej witaminy C.

Polish has no articles, so lekarz can mean doctor, a doctor, or the doctor depending on context.

In this sentence, Lekarz mówi... is most naturally understood as The doctor says... because the situation probably makes it clear which doctor is meant.

Also, Lekarz is capitalized here only because it is the first word of the sentence. Normally, lekarz is not capitalized.

Że means that and introduces a subordinate clause.

So:

• Lekarz mówi = The doctor says
• że potrzebuję więcej witaminy C = that I need more vitamin C

Just like in English, that can sometimes be omitted in translation, but in Polish że is very commonly kept.

Mówi is the 3rd person singular present form of the verb mówić (to speak / to say).

Here it means:

• on/ona mówi = he/she says

Since lekarz is singular, the verb must also be singular:

• Lekarz mówi = The doctor says

A useful mini-pattern:

• mówię = I say / I am speaking
• mówisz = you say
• mówi = he/she says
• mówimy = we say
• mówicie = you all say
• mówią = they say

Yes. Potrzebuję means I need, and the -ę ending shows 1st person singular.

The infinitive is potrzebować = to need.

So:

• potrzebuję = I need
• potrzebujesz = you need
• potrzebuje = he/she/it needs

Because the verb ending already tells you the subject, Polish usually does not need the pronoun ja.

So:

• potrzebuję więcej witaminy C = I need more vitamin C

You could say ja potrzebuję, but that adds emphasis, like I need...

Polish often drops subject pronouns because the verb ending already tells you who the subject is.

Here, potrzebuję clearly means I need, so ja is unnecessary.

Compare:

• potrzebuję = I need
• ja potrzebuję = I need / I need

The version with ja sounds more emphatic or contrastive.

Because więcej (more) is followed by the genitive case.

So after więcej, the thing you want more of must change form:

• nominative: witamina C = vitamin C
• genitive: witaminy C = of vitamin C

That is why the sentence has:

• więcej witaminy C = more vitamin C

This same pattern happens with many quantity words:

• dużo wody = a lot of water
• mało czasu = little time
• więcej pieniędzy = more money

Because witamina is a normal noun and declines by case, while C here is just the letter name used as part of the expression witamina C.

So:

• witamina C = nominative
• witaminy C = genitive

Only witamina changes form. The C stays the same.

This is similar to how some fixed labels, symbols, or letter names remain unchanged in expressions.

Traditionally, yes: potrzebować is a verb that takes the genitive.

That matches what you see here:

• potrzebuję witaminy C = I need vitamin C

In this sentence, there is also więcej, which independently also requires the genitive, so the genitive is definitely expected.

So the phrase works neatly as:

• potrzebuję więcej witaminy C

For a learner, the safest rule is: after potrzebować, expect the noun to appear in the genitive.

The basic order is:

• Lekarz = subject
• mówi = verb
• że... = subordinate clause
• potrzebuję więcej witaminy C = the content of what is being said

So the sentence is very standard and neutral: Lekarz mówi, że potrzebuję więcej witaminy C.

Polish word order is more flexible than English, but changing it usually changes emphasis, not core meaning. For example, you might move więcej or witaminy C for focus, but the given version is the most neutral and natural for learners.

A rough guide:

• że sounds roughly like zheh, with ż like the s in measure
• potrzebuję is roughly po-tshe-BU-yeh

A few details:

• rz often sounds like zh
• cz sounds like ch in chop
• final -ję in potrzebuję is often pronounced something like -ye

So:

• potrzebuję ≈ po-tsheh-boo-YEH

The nasal vowel ę does not sound exactly like any normal English vowel, and in real speech its pronunciation changes depending on position. You do not need to master all its phonetic details immediately to understand the sentence.

Both can relate to saying, but they differ in aspect.

• mówić = imperfective, focuses on the act/process or general statement
• powiedzieć = perfective, focuses on saying something as a completed act

So:

• Lekarz mówi, że... = The doctor says that...
• Lekarz powiedział, że... = The doctor said that...

In your sentence, mówi presents it as a current statement or general report. A learner can think of it as the natural present-tense choice.

Yes. Iż is another word meaning that, similar to że.

However:

• że is much more common in everyday speech
• iż sounds more formal, literary, or stylistically marked

So for normal conversation, że is the better choice.

No. Więcej can be used with both countable and uncountable nouns.

Examples:

• więcej jabłek = more apples
• więcej wody = more water
• więcej witaminy C = more vitamin C

So it works well here even though vitamin C is being treated more like a substance or nutrient than a countable item.