In today’s newsletter: When it comes to salt, there can be too much of a good thing. But how much salt is that, exactly? Plus, how do microplastics harm humans? Also, when does old age begin and why you may want to skip that nightcap before bed. 

PHOTOGRAPH BY JOZEF VACLAVIK, GETTY IMAGES

Ah, salt. Perhaps one of the most beloved condiments for good reason. It’s tasty, enhances our food and is also an essential nutrient.
 
Yet salt can be the source of serious diseases, like high blood pressure, when consumed in excess—which is why you might be surprised to learn that scientists are locked in a bitter debate over how much salt is too much. The answer isn't as clear as you might think. 

Related: 
— The 7 hormones that influence how much—or little—you eat

PHOTOGRAPH  BY ALEXANDER STEIN, JOKER/ULLSTEIN BILD/GETTY IMAGES

PLASTIC ALL OVER: As plastic waste proliferates around the world, an essential question remains unanswered: What harm, if any, does it cause to human health?

Related:
— Our car tires are poisoning salmon—and maybe us, too

PHOTOGRAPH BY MATTHIEU PALEY, NATIONAL GEOGRAPHIC IMAGE COLLECTION

PHOTOGRAPH BY GREGOR LENGLER, LAIF/REDUX

Sleep is vital for your brain health—think of it as a rinse cycle for your brain. But a study suggests that common sleep aids may interfere with one of the mysterious processes that clears out the brain’s molecular trash at night.

ONE LAST THING: Having a nightcap before bed? You might want to rethink that... 

Today’s newsletter was edited and curated by Jennifer Baik and produced by Alisher Egamov. Did someone forward this to you? Sign up here to get this newsletter and more.