- With Mayo Clinic nutritionist
Katherine Zeratsky, R.D., L.D.
read biographyclose windowBiography of
Katherine Zeratsky, R.D., L.D.
Katherine Zeratsky, R.D., L.D.
As a specialty editor for the Food & Nutrition Center, Katherine Zeratsky helps you sort through the facts and figures, the fads and the hype to learn more about nutrition and diet.
A Marinette, Wis., native, she is certified in dietetics by the state of Minnesota and the American Dietetic Association. She has been with Mayo Clinic since 1999.
She is active in nutrition-related curriculum and course development in pediatrics at Mayo Clinic Rochester and nutrition education related to the physiology and recommended intakes for premature infants.
Other areas of interest include breast milk and formula safety, neonatal feeding, and nutrition for breast-feeding mothers.
She graduated from the University of Wisconsin-Madison, served a dietetic internship at the University of Iowa Hospitals and Clinics, and worked as a registered dietitian and health risk counselor at ThedaCare of Appleton, Wis., before joining the Mayo Clinic staff.
More answers
- Food poisoning: How long can you safely keep leftovers?
- Water softeners: How much sodium do they add?
- Fiber supplements: Are they safe to take every day?
- Olive oil: What are the health benefits?
- Fat grams, calories or percentages: Which are more important?
- Moldy cheese: Is it unsafe to eat?
- Phenylalanine in diet soda: Is it harmful?
- White whole-wheat bread: Is it nutritious?
- Canned food: How long can you safely keep it?
- Microwaving plastic: Does it release dioxins?
- Stevia: Is it available in the United States?
- Calcium supplements: Do men need them too?
- What is BPA? Should I be worried about it?
- Calcium supplements: Which type is best?
- Thanksgiving turkey: Can you cook it frozen?
- High-fructose corn syrup: What are the concerns?
- Diverticulitis diet: Can certain foods trigger an attack?
- Vitamin D: How much do I need?
- Multivitamins: Do young children need them?
- Buying beef? A guide to choosing the leanest cuts
- Calcium supplements: Should they be taken with meals?
- Low-sodium diet: Why is processed food so salty?
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- High-protein diets: Are they safe?
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- Vegetable juice: As good as whole vegetables?
- Butter vs. margarine: Which is better for my heart?
- Acai berry products: What are the health benefits?
- Percent Daily Value: What does it mean?
- Coffee and health: What does the research say?
- Detox diets: Do they offer any health benefits?
- Freezing meat: Does it kill harmful bacteria?
- Chocolate: Does it impair calcium absorption?
- Energy drinks: Do they really give me energy?
- Vitamin C: Can too much be harmful?
- Alkaline water: Does it have health benefits?
- Canola oil: Does it contain toxins?
- Dietary supplements vs. food: Which is better?
- E. coli: How can I tell if food is contaminated?
- Roasting nuts: Lower fat by roasting in the shell?
- Yerba mate: Is it safe to drink?
- Water after meals: Does it disturb digestion?
- Ground flaxseed: Better than whole?
- Diverticulitis diet: Should I avoid nuts and seeds?
- Monosodium glutamate (MSG): Is it harmful?
- Canned pumpkin: Better than fresh?
- Smart Balance: Are cholesterol-lowering products safe for everyone?
- Vitamin water: Better than plain water?
- Diet soda: Is it bad for you?
- Microwave popcorn: Is it linked to lung disease?
- Too skinny? How to add pounds safely
- Sea salt vs. table salt: Which is better?
- Caffeine: Is it dehydrating or not?
- Prenatal vitamins: OK for women who aren't pregnant?
- Grape juice: Same heart benefits as wine?
- Diverticulitis diet: What should I eat after an attack?
- Lentils: How do I cook with them?
- see all
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Question
Vitamin D: How much is too much?
Is it possible to take too much vitamin D? I know vitamin D is important, but I wonder if too much is dangerous?
Answer
from Katherine Zeratsky, R.D., L.D.
Vitamin D is an essential nutrient for your entire body. Still, it's possible to have too much of a good thing.
Vitamin D has long been known to promote healthy bones. Some research suggests that vitamin D may also help prevent certain cancers, as well as diabetes, high blood pressure, multiple sclerosis and various other conditions.
Vitamin D is naturally present in some foods and is added to others. It is also available as a dietary supplement. The best food sources of vitamin D include salmon, mackerel, sardines, tuna and fortified milk. Cod liver oil also contains large amounts of vitamin D. Vitamin D is also produced by the body, triggered by sunlight on the skin.
Recent research suggests that many people may not be getting enough vitamin D. More exposure to sunlight can help, but this increases the risk of skin cancer and other skin problems. The National Academy of Sciences currently recommends 200 international units (IU) of vitamin D a day for children and adults up to age 50. This is about the amount of vitamin D in 3 ounces of tuna or 16 ounces of fortified milk. For adults older than age 50, the recommendation increases to 400 to 600 IU a day. If you're not getting enough vitamin D, your doctor may recommend vitamin D supplements. Still, moderation is important.
You're unlikely to get too much vitamin D from the food you eat, and prolonged sun exposure doesn't seem to cause vitamin D toxicity. Over time, however, megadoses of vitamin D supplements can cause nausea, vomiting, poor appetite, constipation, weakness and weight loss. More seriously, excessive doses of vitamin D can raise the level of calcium in your blood — which can cause confusion and changes in heart rhythm. Generally, the upper limit for vitamin D is 2,000 IU a day.
If you're concerned that you're getting too little — or too much — vitamin D, contact your doctor. He or she may recommend a blood test to check the level of vitamin D in your blood.
Next questionFood poisoning: How long can you safely keep leftovers?
- Dietary supplement fact sheet: Vitamin D. Office of Dietary Supplements. http://ods.od.nih.gov/factsheets/vitamind.asp. Accessed May 28, 2008.
- Hathcock J, et al. Risk assessment for vitamin D. American Journal of Clinical Nutrition. 2007;85(1):6-18.
- Holick M. Vitamin D deficiency. New England Journal of Medicine. 2007;357(3):266-281.
- Wagner CL, et al. Prevention of rickets and vitamin D deficiency in infants, children, and adolescents. Pediatrics. 2008;122(5):1142-1152.
