Okay since everyone seems to still be confused on the whole apple thing...

In episode 1 they revealed that he suffers from Vasoconstriction:

Vasoconstriction is the narrowing (constriction) of blood vessels by small muscles in their walls. When blood vessels constrict, blood flow is slowed or blocked. Vasoconstriction may be slight or severe. It may result from disease, drugs, or psychological conditions.

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There are some Vasodilators medications that are used for moderate / severe cases when the typical blood pressure medicines don't provide much help. These however come with a lot of side effects.

The skin of red apples have chemical compounds that act as a Vasodilator without the side effects, works quickly and can work in conjunction with other blood pressure medications.

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To put it in context that might be easier for people to understand:

It's like someone that has asthma and is on a once daily/weekly medication but still needs to use a rescue inhaler for sudden acute asthma attacks. Sun is most likely on medication for his Vasoconstriction, but still needs the Red Apple skin for the sudden acute attacks. That's why you see him taking bites from around the apple instead of eating the whole thing, the skin is the most important part for him.

Thank you! That helps a lot.

I for one used to say... apples? Really? But when I read your comment it made a lot of sense.  Let's hope people see this discussion and stop with the apple thing from now on! 

Thanks so much for this explanation! This could have been explained better in the show, but in thinking about it.... Sun hasn't spoken to anyone about his specific medical condition yet... He's still a lonely person.

 rainycloud:

Thanks so much for this explanation! This could have been explained better in the show, but in thinking about it.... Sun hasn't spoken to anyone about his specific medical condition yet... He's still a lonely person.

yeah just that brief mention to his friend in ep 1 and his mother saying how important red apples are to him, but never going into detail as to why.

Major oversight on the writer / director's side

That's a valiant attempt at explaining it, but the amount in a red apple skin is so vanishingly low it will do nothing for you in an attack, not to mention that it would take quite a while to digest it enough to get into your bloodstream. I googled the topic before replying, and do you know what one of the first hits was? Your post! You'll probably end up being a Wikipedia reference now, so I hope your ready for the responsibility.

Anyway, there's enough truth in it to justify it as part of the story, but anyone with vasoconstriction, see a cardiologist and don't rely on apples to save you.

 jpny01:

That's a valiant attempt at explaining it, but the amount in a red apple skin is so vanishingly low it will do nothing for you in an attack, not to mention that it would take quite a while to digest it enough to get into your bloodstream. I googled the topic before replying, and do you know what one of the first hits was? Your post! You'll probably end up being a Wikipedia reference now, so I hope your ready for the responsibility.

Anyway, there's enough truth in it to justify it as part of the story, but anyone with vasoconstriction, see a cardiologist and don't rely on apples to save you.

They are severely overexaggerating his attacks in this, the medication his cardiologist would prescribe would be the main thing to control the condition. The Red Delicious apple skin is more for the chest pains, tightness, and pressure spikes that do come on suddenly. It actually doesn't take that long after ingesting for it to start helping, it depends on the person, severity, etc. but it starts to help around 15-30 minutes normally.

That's so weird that this was one of the first hits when googling it. Then again when I was cross referencing with the medical study it did take a bit to find it.