Very high triglycerides can be caused by poor diet and not enough exercise. You may also have inherited very high triglycerides from a parent. Your doctor will tell you how to manage your triglycerides. If your weight is higher than what is considered healthy, losing even 5 pounds may help lower your triglycerides.
WORD likes it un-hyphenated but I don't. Long-term should be hyphenated but longtime should not be hyphenated, at least until a few more decades pass and the grammatical rules for the use of hyphens either relax or fade away. Here is part of an erudite commentary on this subject:
Definition: Two or more words (such as part-time or high-speed) that act as a single idea to modify a noun (a part-time employee, a high-speed chase). Also called phrasal adjective or compound modifier. As a general rule, the words in a compound adjective are hyphenated when they come before a noun (a well-known actor) but not when they come after (The actor is well known). Also, compound adjectives formed with an adverb ending in-ly (such as rapidly changing) are usually not hyphenated.