DEAR DR. BLONZ: We just moved to a "hard-water" area that relies on a water softener to keep appliances from getting over-mineralized. Do I need to bypass softened cold water for drinking? How much sodium does one get from softened water, and is it a problem? Does the Brita filter remove sodium? Nobody in the family has issues with high blood pressure. -- E.A., Madison, Wisconsin

DEAR E.A.: The level of minerals in a given water supply varies by geographical location and by how the water gets processed before being consumed. Water with higher concentrations of calcium, magnesium and other minerals is said to be "hard." (For more about geography and water hardness, see b.link/dyjJfm.) Typically, there isn't enough of these minerals to make the water a significant dietary source, but hard water can leave mineral deposits in water pipes and fixtures, on pots and pans, on appliances such as water heaters, coffee makers and tea kettles, and can leave mineral spots on glassware and soap film in the tub and shower.

Water softeners work by exchanging sodium for the water's naturally occurring calcium and magnesium. Sodium is more soluble; the resulting water is said to be "soft." In addition to not leaving mineral deposits, soft water works better with detergents, so your clothes get cleaner. One study at Purdue University found that clothing and household textiles last about 15% longer when washed in soft water.

The amount of sodium in softened water varies because of the level of minerals being replaced; the higher the initial concentration of minerals, the greater the amount of sodium after softening. It is generally not that much, but check with your water softener company to determine the level of minerals in your area and how much sodium would end up in your softened water. For a general perspective, hard water that starts with 15 grains of minerals per gallon will end up with the equivalent of 28 mg of sodium per cup after softening. Given the dietary guideline to stay below 2,300 mg sodium per day, this would make softened water a very low source. This could be an issue for someone on a strict low-sodium diet, so be aware of what is in your water supply and how your softener operates, and check with your health professional. Water-pitcher filters, such as the Brita brand, do not remove sodium from softened water.

It's good news that your family has no problems with blood pressure. While hard water is considered better to drink, one option is to have the house-water softener connected only to the hot-water line. You could also use potassium salts or a mix of sodium and potassium rather than straight, sodium-based softening salts. Another option is to use a reverse osmosis device to remove the sodium from the softened water. Finally, while on the topic, softened water might not be ideal for certain plants, so find out if there might be an issue with what's growing at your place.

Send questions to: "On Nutrition," Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: I keep seeing messages that foods are now mineral-deficient, and we need supplements to prevent deficiencies. Which minerals are currently believed to be essential for good health? Are there still as many of these as there used to be, or has modern agriculture made it so foods have less? -- T.S., San Diego

DEAR T.S.: A mineral is loosely defined as anything in nature that is not animal or vegetable. Minerals are inorganic chemical elements required for specific structures or metabolic functions; "inorganic" means they do not contain the element carbon. The body cannot synthesize or change minerals; they don't provide calories and are needed only in small amounts relative to protein, fat and carbohydrate. The body can become more efficient in recycling some nutrients; still, prolonged insufficient intakes lead to a failure to thrive and the development of deficiency diseases, the expression of which depends on the nutrient.

Minerals needed in more significant amounts include calcium, chloride, magnesium, phosphorous, potassium and sodium. Chromium, copper, fluoride, iodine, iron, manganese, molybdenum, selenium and zinc are equally essential, but needed only in trace amounts. (Check the National Library of Medicine's page on minerals at b.link/5wfsdv.) All the minerals the body needs can be found in food.

Think of plants as miners, pulling the mineral elements out of their environment, unable to grow and thrive if an essential mineral is absent. It follows that essential minerals that leave with the plant at harvest need to be replaced using fertilizer or compost, or subsequent yields will drop.

Minerals that are not essential for the plant can also end up in the food; what enters can vary by mineral, soil and weather -- even among different varieties of the same fruit, vegetable or grain. The plant's overall nutrient content can also vary by the length of time the plant has had to grow. Although the differences might not be significant, a plant picked green that ripens after harvest may not have the same total nutrient content as one allowed to ripen "on the vine."

For example, whole foods grown in iodine-rich or selenium-rich soils tend to have more of these nutrients than the same type of food grown in soils with lesser amounts of these minerals. Of historical interest, iodine-rich soils tend to be close to the coast, with less iodine found in foods grown inland. The incidence of goiter, an expression of iodine deficiency, once correlated with distance from the coast and led to the introduction of iodized salt in 1924. The typical diet in the U.S. is now iodine-sufficient, so iodized salt is no longer needed.

While we may have turned to varieties better suited to transportation and storage, it is incorrect to say today's fruits, vegetables or grains will provide any fewer essential nutrients than the same varieties would have provided in the past. Nutrient data tables, such as those provided by the USDA, present the nutrients expected in a particular food (fdc.nal.usda.gov/). Finally, check the source of the "foods are now mineral-deficient" messages you're seeing; aside from being misleading, you may find they originated from a party seeking to sell supplements.

Send questions to: "On Nutrition," Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: Please explain the change in nutrient demand, and how the kidneys change, during pregnancy. -- P.O., Arlington Heights, Illinois

DEAR P.O.: Nutrient requirements increase before and during that marvelous construction project, but that also includes an increased production of metabolic waste products. It's all part of making the mother's body ready to house, nurture and protect the developing fetus, and have tissues prepared to create and provide nourishment for the baby after birth. There are also pre-pregnancy nutrition advisories, so be sure to check with your physician, as you may be advised to begin a prenatal supplement a few months before even trying to get pregnant.

Blood is the body's primary transport network, carrying nutrients, raw materials, control substances where needed and energy substances on their way to or from storage. The blood is also the conduit for metabolic wastes needing transport on the way to elimination.

The kidneys serve as the blood's cleansing filter, and are also responsible for fine-tuning the concentration of various substances in the bloodstream. The body adapts to its increased needs during pregnancy by increasing its blood volume; this allows greater amounts of the nutrients and waste products involved in pregnancy. The hormonal changes during pregnancy raise the blood flow through the kidneys and increase their size to handle the greater responsibilities. Staying well hydrated is essential, but the developing fetus does mean less room for the urinary bladder, leading to the need to relieve oneself more frequently.

DEAR DR. BLONZ: I would like to know the benefits of biotin. Would everyone get some benefit when taking this vitamin? -- E.B., Palo Alto, California

DEAR E.B.: Biotin, also known as vitamin B7, plays an essential role in the metabolism and synthesis of fats, amino acids and carbohydrates. Although essential, biotin is needed only in small amounts. The recommended dietary allowance for adults is 30 micrograms (mcg) per day. (Check the National Institutes of Health fact sheet on biotin at b.link/xd27x7.) Foods that contain biotin include organ meats, oatmeal, egg yolk, milk, soybeans, peanuts, whole grains, fruits and vegetables. Biotin can also be synthesized by bacteria in our microbiome, but it is unclear how much of this we absorb.

An interesting side note: Egg yolks are a good source of biotin, but a compound in raw egg whites, named avidin, prevents biotin from being absorbed. Avidin is destroyed by boiling and other forms of cooking. Biotin deficiencies have been found in individuals who consume large quantities of raw egg whites. Raw eggs are a favorite food of foxes, but they pay the price of overindulgence with a biotin deficiency, which is nature's way of keeping the fox out of the hen house.

Send questions to: "On Nutrition," Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.