Those first strands of gray hair are a sign of the inevitable. We’re getting older and our bodies are changing. We may grow a little rounder around the waistline, or wake in the night, or feel a little stiffer in the morning. Yet while we adapt to new realities, we shouldn’t discount every symptom as just further evidence of aging.

How do you know when to ignore your body’s lapses or when to seek medical advice? What’s normal aging, and what’s not?

“Aging, in and of itself, is a subtle, quiet process,” says Marie Bernard, MD, deputy director of the National Institute on Aging. If you have a sudden change or if you feel pain, that is a red flag, she says.

“I’ve had many a patient come in and complain about pain in the knee. They’ve said, ‘It’s just my age,’” says Bernard, a geriatrician. “The reality of the matter is both knees are the same age. Why is one knee painful and the other is not?”

We shouldn’t think of aging as a failure of our bodily systems, says Kenneth Minaker, MD, chief of geriatric medicine at Massachusetts General Hospital in Boston and associate professor of medicine at Harvard Medical School. “Aging is a life-saving process,” he says. “It is a process of lifelong adaptation to prevent us from developing cancers that would kill us.”

Natural changes in cells may slow them down or alter their capacity, he says. Most people reach their peak functioning at around age 30.

How soon you notice age-related changes in stamina, strength, or sensory perception will vary based on your personal health choices, your medical history, and your genetics, Minaker says.

Your access to medical care and education, income, neighborhood, and community may also play a role in your health. These are what experts call “social determinants of health” among groups of people. Social determinants of health can lead to health disparities. The CDC defines health disparities as “preventable differences in the burdern of disease, injury, violence, or opportunities to achieve optimal health that happen in socially disadvantaged groups.” For instance, certain conditions – like diabetes and high blood pressure – are more common in some minority groups than among white people.

Some age-related complaints are common, and some symptoms aren’t caused by aging at all. Here is some advice on how to tell the difference:

By around age 40, almost everyone will be reaching for reading glasses. Presbyopia occurs when the lens becomes stiff and won’t adjust to refocus from distance to near vision. Cataracts, or clouding of the lens, may begin to affect your vision when you reach your 60s. Long-term exposure to sunlight increases the risk of cataracts, which can be corrected through surgery to replace the lens.

If you notice you have worse peripheral than central vision, or the reverse, you could have a serious eye condition that requires treatment. Glaucoma occurs when the pressure in the eye increases and causes damage to the optic nerve. Two forms of macular degeneration affect the center of the retina, leading to a loss of central vision.

The bottom line: “If you feel you’re having blurred vision or vision loss, you should get your eyes examined,” says Hilary Beaver, MD, associate professor of clinical ophthalmology at the Weil Cornell Medical College at The Methodist Hospital in Houston. It’s a good idea to have preventive checkups, too, especially if you have diabetes or a family history of glaucoma or macular degeneration, she says.

About a third of people who are 60 or older have some hearing loss. This condition, known as presbycusis, may be due to the loss of sensory receptors in the inner ear. At first, some sounds may seem muffled, and high-pitched voices may be harder to understand. Men tend to have more hearing loss than women.

Pain, drainage from the ear, or a rapid loss of hearing could be a sign of a tumor or infection, cautions Robert Dobie, MD, professor of otolaryngology at the University of Texas Health Science Center in San Antonio. If the hearing in one ear is noticeably worse than the other, that is also a reason to have it examined, he says.

“If people just notice, ‘I’m not hearing quite as well as I did a few years ago,’ that’s the aging process,” Dobie says. “If I don’t hear as well this week as I did last week, that’s not the aging process.”

With age, we lose muscle tissue and our muscles become more rigid and less toned. Weight training and stretching improve strength and flexibility, though we can’t completely counteract this natural course of aging.

Our organs lose their extra reserve, too. The walls of the heart become thicker, the arteries are stiffer, and the heart rate slows as we age. Aging of the heart is a major reason it may be harder to exercise vigorously when we are older as we could when we were 20. Yet maintaining regular aerobic activity — even just walking — can improve our stamina.

When should you worry? Get an immediate evaluation if you have chest pain, especially with dizziness, nausea, shortness of breath, or fainting. Those are possible signs of a heart attack. Problems with your heart rate could cause lightheadedness, dizziness, or fatigue.

One in 10 people age 65 or older have anemia, or a low level of oxygen-carrying red blood cells. It can cause fatigue and can be treated with iron supplements or medications to spur the body to produce more red blood cells.

Aging is not a disease, but our body’s changes make us vulnerable to some medical conditions.

One example is essential hypertension, or high blood pressure. The exact cause of essential hypertension is not known. There are several factors that play a role including genetic factors, obesity, salt intake and aging. Blood vessels tend to become less elastic with age, and this stiffness may contribute to high blood pressure.

More than half of people 60 and older have high blood pressure – a reading of 130 (systolic) over 80 (diastolic) or higher.

A low-sodium diet, exercise, and maintaining a healthy weight can help prevent high blood pressure.

Can’t remember where you put your keys? Forgot the name of an acquaintance you haven’t seen in a while? Those momentary lapses are normal.

No need to worry, unless the forgetfulness is impairing your daily life, says John Q. Trojanowski, MD, PhD, co-director of the Center for Neurodegenerative Disease Research and professor of geriatric medicine and gerontology at the University of Pennsylvania in Philadelphia. “Many of us have a memory complaint, but it’s not dementia or disease,” he says.

Generally, information processing slows as we grow older, and older people have more trouble multitasking. But there’s a lot of variability in cognitive function. Not surprisingly, for example, older adults typically outperform young adults in their knowledge of the world.

The red flag for dementia related to Alzheimer’s disease is the inability to learn and retain new information. Problems with episodic memory are a sign of mild cognitive impairment that could be a precursor of the disease, according to new guidelines for diagnosing Alzheimer’s.

People with Alzheimer’s have other cognitive deficits, as well, such as trouble with language or recognizing objects, Trojanowski says. Biomarkers detected through imaging or a test of cerebrospinal fluid can aid in the diagnosis of Alzheimer’s.

If you have memory problems and you have a family history of Alzheimer’s disease, you may want to be evaluated. Alzheimer’s disease rarely occurs among people who are younger than 65. About one in eight people aged 65-74 have Alzheimer’s, and 43% of people who are older than 85 have Alzheimer’s.