Too much of a good thing can be bad

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We've all heard that moderation is the key to good health. It's also great for the environment since moderation equals less consumption and therefore less stress on the planet.

But aren't there some things that you just can't have too much of? Not really. Even things that are good for you can be damaging if you consume too much. Below are some surprising examples.

Vitamin C is an essential nutrient that needs to be ingested every day because our bodies don't produce or store it. What your body doesn't need is flushed out in your urine, but it's still possible to take too much. Mega-doses of vitamin C can cause gastritis, nausea, diarrhea, and kidney stones, according to the Mayo Clinic. In rare cases it can make you tired and dizzy.

The recommended daily allowance is 75 milligrams a day for women, 90 mg for men.  You can likely have more without feeling sick, but adults should not consume more than 2,000 mg in a day. Some good food sources: half cup chopped raw sweet red peppers (141 mg), one cup of strawberries (82 mg), six ounces of orange juice (75 mg), a medium orange (70 mg).

Protein helps build muscle, blood, skin, hair, nails, and more. There is a long list of health benefits associated with eating proper amounts of protein from providing energy to keeping the immune system in good shape. But eating too much protein can cause kidney problems, dehydration, and osteoporosis, and it may be linked to certain cancers.

How much is just right? Here are some guidelines from Harvard University for calculating how many grams of protein you should eat a day based on your weight. In general, you shouldn't get more than 20 to 25 percent of your daily calories from protein.

Soybeans are popular because they boast many health benefits from lowering cholesterol to reducing the risk of certain types of cancer, but that doesn't mean you should eat soy foods with abandon. Some compounds in soybeans mimic the hormone estrogen. Animal studies suggest that large amounts of soy might reduce fertility in women, trigger early puberty, and disrupt development in fetuses and children.

No one is suggesting you banish soy foods from your diet, just eat them in moderation. A high soy diet is considered 25 or more grams per day. If you eat a lot of soy products, you might want to ask your doctor for advice on what your maximum daily intake should be. 

Exercise is something most of us don't get enough of. About 30 minutes of moderate exercise a day is enough to ward off chronic diseases such as diabetes, improve mood, and deliver a whole bunch of health benefits. Shoot for at least 60 minutes a day, 5 to 6 times a week if you want to get the most benefits from exercise.

Is there such a thing as too much exercise? Yes, and it can lead to injuries, exhaustion, depression, and long-term health problems.

It is entirely possible to become addicted to exercise, which is definitely not healthy. You know you're exercising too much when exercise starts taking over your life (you organize your life around exercise as opposed to organizing your exercise to fit into your life). Other strong indications: You get injured often or are left feeling exhausted and depleted after workouts instead of rejuvenated.

Fluoride, which is found naturally in water and is also added to many municipal supplies, is a major weapon against tooth decay. If kids under 8 years of age get too much, though, they may develop enamel fluorosis, which causes their permanent teeth to become discolored or mottled.

What can you do to protect your child's teeth? Don't use more than a pea-sized amount of fluoride toothpaste and avoid using fluoride mouth rinse for kids unless your dentist recommends it. Here are some additional guidelines from the Centers for Disease Control and Prevention for reducing the risk of flourosis.

The same rules apply for things that are traditionally thought of as being bad for you. Moderate amounts of dark chocolate, coffee, and red wine can be good for you, so go ahead and indulge every now and then.

Environmental journalist Lori Bongiorno shares green-living tips and product reviews with Yahoo! Green's users. Send Lori a question or suggestion for potential use in a future column. Her book, Green Greener Greenest: A Practical Guide to Making Eco-smart Choices a Part of Your Life is available on Yahoo! Shopping and Amazon.com.

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