Please summarize this article in less than 5 sentences with all its key points:

"Loud snoring may be a harbinger of much bigger problems, research out this week suggests. The study found a link between severe sleep apnea in older adults and greater amounts of a specific biomarker in the brain—one that could increase people’s risk of dementia or stroke. More research will be needed to understand this connection, however.  Sleep apnea is a condition in which a person stops breathing during sleep. This causes the brain to wake the person just enough to start breathing, only for the cycle to start again once the person falls back asleep. There are two main forms of sleep apnea, obstructive and central. Obstructive apnea happens when airway muscles physically block a person’s breathing, while central apnea is when the brain forgets to signal the body to breath (a third mixed form has features of both).

Though not all snoring is linked to obstructive sleep apnea, it’s a common sign of the condition (snoring in general is caused by a narrow airway while sleeping). The constant interruptions caused by apnea also make it hard for people to get a restful night’s sleep, which can then affect their physical and mental health in varying ways.  Sleep apnea, especially when severe, has been linked to a greater risk of many other health problems, including cardiovascular disease. In this new study, published Thursday in the journal Neurology, scientists wanted to get a better understanding of how the condition could possibly affect the brain.  They looked at data collected from 140 older adults with obstructive sleep apnea who had participated in an earlier study. These volunteers had undergone an MRI brain scan and were monitored overnight in a sleep lab. They were divided into three groups based on their diagnosed degree of sleep apnea, but all of them were thought to be free of dementia at the start and end of the study period."
Here are the key points from this article:

A study has found that sleep apnea can lead to very serious health problems, specifically in older adults. Firstly, there are three types of sleep apnea - obstructive, central, and a mix of both. Obstructive is when airway muscles block someone's breathing, and central is when the brain doesn't send signals to the body to breathe. The health risks include cardiovascular disease, dementia, or even strokes depending on the severity. The constant interruptions in sleep keep them from getting restful sleep which leads to these issues.