Takviye alerji belirtilerini artırdı.

A natural breakdown is:

• takviye = supplement
• alerji = allergy
• belirtilerini = the allergy symptoms
• artırdı = increased

A more detailed breakdown of belirtilerini is:

• belirti = symptom, sign
• -ler = plural
• -i = the noun-compound ending here
• -ni = accusative ending, marking it as the direct object

So the structure is basically:

[Subject] [Object] [Verb]
Takviye / alerji belirtilerini / artırdı

Because Turkish usually uses Subject + Object + Verb as its neutral word order, and that is what you have here.

Also, belirtilerini has object marking on it, so it is clearly the direct object. That leaves takviye as the subject.

So the sentence is understood as:

• takviye = the thing doing the action
• alerji belirtilerini = the thing affected by the action
• artırdı = the action

That -ni is the accusative ending on a possessed/compound noun form. In this sentence, it marks alerji belirtilerini as a specific direct object.

A very common Turkish pattern is:

• unmarked object = non-specific / general
• accusative-marked object = specific

Here, the sentence is talking about a particular set of allergy symptoms, so the object is marked.

Because the word already has an -i before it, the accusative appears as -(n)I, giving:

• belirtileri
  • -ni = belirtilerini

In this sentence, it is part of the noun compound structure.

Turkish often forms expressions like allergy symptoms, coffee cup, school bus with a noun + noun pattern. In that pattern, the second noun usually takes an ending like -(s)i.

So:

• alerji belirtisi = allergy symptom
• alerji belirtileri = allergy symptoms

That -i looks like a 3rd-person possessive ending, and historically it is related, but in sentences like this it is best to think of it as part of the standard noun-compound pattern.

Then, because the phrase is the direct object, Turkish adds -ni:

• alerji belirtileri → alerji belirtilerini

Because Turkish often uses a bare noun before another noun to modify it.

So:

• alerji belirtisi = allergy symptom
• kahve fincanı = coffee cup
• okul otobüsü = school bus

The first noun often stays plain, and the second noun carries the compound marking.

That is why you get:

• alerji belirtileri

not an adjective form of alerji.

Because alerji belirtileri and alerjinin belirtileri are similar, but not the same.

• alerji belirtileri = allergy symptoms
  This is a general noun-compound expression.
• alerjinin belirtileri = the symptoms of the allergy
  This sounds more like you are referring to a specific allergy in a more explicitly possessive way.

So in your sentence, alerji belirtilerini is the more natural way to say allergy symptoms as a standard medical-type phrase.

Artırdı is the simple past tense of artırmak, which means to increase something.

Breakdown:

• artır- = increase
• -dı = past tense

So:

• artırdı = increased

It is 3rd person singular, and in Turkish that form does not need an extra ending here. Depending on context, it can mean:

• he increased
• she increased
• it increased

In this sentence, it is it increased, referring to takviye.

That is because of two regular Turkish sound rules:

1. Vowel harmony
   The past tense suffix is basically -DI, but the vowel changes:

   • -dı
   • -di
   • -du
   • -dü

   Since the preceding vowel in artır- is ı, the suffix becomes -dı.

2. Consonant voicing The suffix can begin with d or t depending on the previous sound.
   Since artır- ends in r, which is voiced, the suffix uses d, not t.

So:

• artır-
  • -dı = artırdı

This is a very useful distinction:

• artmak = to increase, to go up
  something increases by itself
• artırmak = to increase something
  someone/something causes it to increase

Examples:

• Belirtiler arttı. = The symptoms increased.
• Takviye belirtileri artırdı. = The supplement increased the symptoms.

Your sentence uses artırmak because the supplement is causing the increase.

Turkish does not use articles the way English does.

So takviye can mean:

• a supplement
• the supplement

depending on context.

For the object, Turkish often shows specificity with the accusative ending instead of a separate word like the. That is one reason belirtilerini feels like the allergy symptoms rather than just allergy symptoms in a vague sense.

So English uses articles, but Turkish often uses:

• context
• case endings
• word structure

instead.

It can change, because Turkish word order is fairly flexible. But Takviye alerji belirtilerini artırdı is the most neutral, straightforward order.

This is the standard pattern:

• Subject + Object + Verb

You could move things around for emphasis, especially because belirtilerini is clearly marked as the object. But the version you have is the best one to learn as the default.

So for a learner, the safest takeaway is:

• Turkish often puts the verb at the end
• this sentence uses the normal, neutral order