1. do
Explanation:

"Do more harm than good" is a common expression meaning to cause more damage than benefits.
Translation: Liều cao của một số loại vitamin có thể gây hại nhiều hơn lợi.

2. far
Explanation:

"Far from improving health" is a phrase used to indicate the opposite of the expected effect.
Translation: Trái ngược hoàn toàn với việc cải thiện sức khỏe, những loại vitamin này khi dùng liều cao...

3. as to
Explanation:

"Unsure as to why" is a common phrase to express uncertainty about a reason.
Translation: Các nhà khoa học không chắc về lý do tại sao vitamin...

4. What
Explanation:

"What this means" is a phrase introducing the interpretation of the preceding statement.
Translation: Điều này có nghĩa là các loại vitamin thương mại...

5. those
Explanation:

"Those provided by nature" refers to the natural vitamins being compared to commercial ones.
Translation: Các loại vitamin được bán thương mại và những loại do thiên nhiên cung cấp...

6. more
Explanation:

"More natural and beneficial" emphasizes the types of nutrients being interfered with by synthetic forms.
Translation: Các dạng vitamin thương mại có thể làm mất đi những loại chất dinh dưỡng tự nhiên và có lợi hơn.

7. from
Explanation:

"Obtained from food" is a standard phrase describing the source of something.
Translation: Các loại vitamin thu được từ thực phẩm...

8. or
Explanation:

"Moderate or augment" provides two possible effects that substances may have.
Translation: Các chất này có thể điều chỉnh hoặc tăng cường hoạt động của vitamin trong cơ thể.

9. is
Explanation:

"The latest advice is to" is grammatically correct to introduce a piece of advice.
Translation: Lời khuyên mới nhất là hãy ăn một chế độ cân bằng...

10. sure
Explanation:

"Make sure" means to ensure that something is done correctly.
Translation: ...và nếu bạn cần bổ sung vitamin, hãy đảm bảo rằng...

Hoàn chỉnh đoạn văn:
Vitamins are good for our health, aren’t they? Perhaps not. New research suggest that rather than ward off disease, high doses of certain vitamins may do more harm than good and could even put you in an early grave. A variety of recent studies suggest that far from improving health, these vitamins, when taken in very high doses, may actually increase the risks of cancer and a range of debilitating diseases, a discovery that has sent the medical world into a spin. Scientists are unsure as to why vitamins, so essential to health, can be toxic in high doses.

The most likely explanation is that the body is only equipped to deal with the levels found naturally in the environment. If the intake is too far above the normal range, then the body’s internal chemistry can be shunted out of alignment. What this means is that the commercially sold vitamins and those provided by nature are not always compatible.

The commercial forms may interfere with the body’s internal chemistry by "crowding out" the more natural and beneficial forms of the nutrients. The vitamins obtained from food are also allied with a host of other substances which may moderate or augment their activity in the body. The latest advice is to eat a balanced diet to ensure you get all the nutrients you need, and if you must take supplements make sure you take the lowest recommended dose and follow the instructions on the bottle.