Learn Hardcore Russian: Витамины помогают телу, а хорошие привычки укрепляют здоровье и настроение. - Vitamins help the body, and good habits strengthen health and mood.

помогать (to help) takes the dative case:
- помогать кому? чему? → телу (to the body)
укреплять (to strengthen) takes a direct object, so accusative case:
- укреплять что? → здоровье, настроение

So:

Витамины помогают телу – Vitamins help (to) the body → телу is dative.
хорошие привычки укрепляют здоровье и настроение – good habits strengthen health and mood → здоровье and настроение are accusative objects.

Because neuter nouns in the singular have the same form in nominative and accusative (здоровье, настроение), they look nominative, but grammatically they’re accusative here.

How do I know that витамины and хорошие привычки are the subjects, not телу, здоровье, or настроение?

You can tell by case and agreement:

Subjects are in the nominative case:
- витамины – nominative plural
- хорошие привычки – nominative plural
Verbs agree with subjects in number:
- витамины помогают – both plural
- хорошие привычки укрепляют – both plural
The other nouns are in object cases:
- телу – dative singular (object of помогать)
- здоровье, настроение – accusative singular (objects of укреплять)

So the “doers” of the actions are витамины and хорошие привычки.

What is the difference between а and и here? Could I say и instead of а?

Both а and и can be translated as and, but:

и simply adds/joins: and, as well as.
а often shows a contrast or slight opposition: whereas, while, on the other hand.

In this sentence:

Витамины помогают телу, а хорошие привычки укрепляют здоровье и настроение.

The idea is:

Vitamins do one helpful thing,
good habits, on the other hand, do another.

If you used и:

Витамины помогают телу, и хорошие привычки укрепляют здоровье и настроение.

That sounds more like a neutral list: vitamins help the body, and (also) good habits strengthen health and mood, without that “contrast / two different categories” feel. Both are grammatically correct; а sounds more natural here because we’re comparing two different helpers.

What aspect and tense are помогают and укрепляют, and when would I use the perfective forms?

помогают – present tense, imperfective aspect of помогать
укрепляют – present tense, imperfective aspect of укреплять

Imperfective in the present is used for:

general truths,
repeated or habitual actions,
ongoing processes.

The sentence is about a general rule, so imperfective is right.

Perfective partners (future only):

помочь → они помогут (they will help once / as a result)
укрепить → они укрепят (they will strengthen as a completed result)

Examples:

Витамины помогут телу – The vitamins will help the body (on that occasion / with that problem).
Эти упражнения укрепят здоровье – These exercises will strengthen your health (as a result).

In your original sentence, you want a general statement, so the imperfective present (помогают, укрепляют) is exactly what you need.

Are здоровье and настроение nominative or accusative here? The forms look the same.

Formally they are accusative singular neuter as direct objects of укрепляют:

укрепляют что? → здоровье, настроение

However, for neuter singular nouns, the nominative and accusative forms are identical:

Nominative: здоровье, настроение
Accusative: здоровье, настроение

So you have to tell the case from function, not form:

After a transitive verb answering что? (what?), it’s accusative.

Why do we say хорошие привычки in the plural? Can I say хорошая привычка instead?

The plural хорошие привычки (good habits) is used because we’re talking about the idea of multiple habits in general influencing health and mood.

Grammatically:

привычка – feminine, singular, nominative.
привычки – feminine, plural, nominative.
хорошая привычка – a good habit (singular).
хорошие привычки – good habits (plural).

You could say:

Витамины помогают телу, а хорошая привычка укрепляет здоровье и настроение.

This would mean:

Vitamins help the body, and a good habit strengthens health and mood.

That sounds more like “any single good habit,” or you’re focusing on one habit, not the whole system of habits. The original sentence is more natural as a health advice statement because good habits (in general) are meant.

How do you pronounce здоровье, and what is that soft sign ь doing there?

Pronunciation: approximately [zda-ROV-ye] in English-style transcription.

More precisely in IPA: [zdaˈrovʲjə]

Syllables:

здо- – [zdo]
ро- – stressed: [ˈrovʲ]
вье – [vʲjə] (with palatalization and a short final vowel)

About ь:

The soft sign ь doesn’t have its own sound.
It softens the preceding consonant (в → вʲ).
In здоровье, it also helps show the [vʲj] cluster before the final vowel.

So здоровье is not zdorovye with a clear ye at the end, but more compact: zda-ROV-ye with a soft v and a quick final vowel.

Do Russians actually say витамин in the singular, or is it mostly used in the plural like here?

Both forms are common; they’re just used in different contexts.

витамин – a vitamin (singular)
- Этот витамин важен для глаз. – This vitamin is important for the eyes.
витамины – vitamins (plural, general talk)
- Витамины нужны всем. – Vitamins are necessary for everyone.

In general claims about health, the plural is more natural:

Витамины помогают телу. – Vitamins help the body.

Literally, you’re thinking of vitamins as a category or group.

Could I use организм instead of тело here? Is there a difference in meaning?

Yes, you can say организм, and it would sound very natural in a health context:

Витамины помогают организму, а хорошие привычки укрепляют здоровье и настроение.

Nuance:

тело – body in a more physical, sometimes neutral or even “just flesh” sense.
организм – organism; in everyday Russian health talk, it often means the whole body as a living system (organs, immune system, etc.).

In health advice, организм is actually more common than тело:

Витамины помогают организму.
Они укрепляют иммунную систему и весь организм.

Your original sentence with телу is still correct and understandable; it just focuses more on the physical body.

Why is there a comma before а?

Because Russian rules require a comma between two independent clauses joined by а.

We have two full clauses:

Витамины помогают телу
(а) хорошие привычки укрепляют здоровье и настроение

Each has its own subject and verb, so they are separate clauses. When they’re linked with а, you must put a comma before а:

…, а … is a standard pattern in Russian punctuation.

Can I change the word order, like Телу помогают витамины or Здоровье и настроение укрепляют хорошие привычки?

Yes, Russian word order is quite flexible, but the neutral pattern is Subject–Verb–Object, which is what you have:

Витамины помогают телу (neutral, standard)
хорошие привычки укрепляют здоровье и настроение (neutral, standard)

Other orders:

Телу помогают витамины.
- Emphasis shifts to телу (“It’s the body that gets help from vitamins”), or you’re contrasting what helps the body.
- Still correct, just with a different focus.
Здоровье и настроение укрепляют хорошие привычки.
- Grammatically possible, but sounds less natural.
- It sounds like you’re emphasizing health and mood first and then revealing who strengthens them.

In ordinary, non-poetic speech, the original word order is best.

Is there a difference between помогают телу and something with a preposition like для тела?

Yes, there is a grammatical and slight meaning difference:

помогают телу – governed by the verb помогать (takes dative):
- literal: help the body or help the body to…
- focuses on the action of helping the body.
для тела – “for the body,” usually used with another verb/adjective:
- полезно для тела – good/beneficial for the body
- важно для тела – important for the body

So:

Витамины помогают телу – Vitamins help the body.
Витамины полезны для тела – Vitamins are good for the body.

You can’t simply replace помогают телу with помогают для тела; that’s incorrect. The preposition для goes with adjectives or other verbs, not with помогать.