Happy birthday! You're 50 years old, so welcome to noticeable changes in your hormone levels, bone density, muscle mass, eyesight, hair, cognition, immunity and more.

"Men increasingly notice the worsening of symptoms that started in their 40s," said Jerry Bailey, an acupuncturist, chiropractic and functional medicine physician at Lakeside Holistic Health.

But what do these changes mean for you?

Here are some fundamental changes you may see in your body after age 50, plus a few tips to help you keep in the best shape possible.

Testosterone continues to decrease

Bailey said once you reach your 50s, you begin to see a severe decline in testosterone levels and a significant increase in estrogen levels.

"This results in fat deposition, breast development, and worsening brain function," he explained.

The debate about why and how your testosterone decreases with age is ongoing. Some professionals, like Bailey, theorize it's because of lifestyle changes.

"These issues are