DEAR DR. BLONZ: Is there any dietary supplement that can help one avoid the misery of poison ivy/oak/sumac? I had heard a vitamin or herb could help, but I would even be open to a prescription medication. Are you aware of anything you can take? -- C.B., via email

DEAR C.B.: I wish it was otherwise, but there are no vitamins or herbs that have been shown to bolster the body's defenses against those peksy poison plants. The rash that develops is a true allergic reaction to the oil called urushiol (oo-ROO-she-awl) found in these plants.

The best defense is avoidance, or some sort of barrier -- be it clothing (that gets carefully handled and double-washed in hot water afterward) or a cream that prevents the oil from coming in contact with your skin. Two commercial products to try are the barrier cream IvyBlock and the cleanup wash Tecnu. These work well for many. Under the "avoidance" banner, remember that pets can be complicit in spreading urushiol around. Cats and dogs often walk in and around the troublesome greenery, and then have little compunction in sharing what they have brushed against.

If you have already been in contact with one of these plants, there are a number of anti-itch products available to help minimize the misery. Contact your physician if you have a nasty case, as there are also prescription medications that can help.

I happen to be one of those unfortunate souls who is hypersensitive to those plants -- just typing this response is making me itch. Parkland surrounds my house, and it is teeming with poison oak. Despite my best efforts, every season I seem to come down with a case of that itchy menace. If there were any vitamin or herb that worked, I would be all over it (and it would be all over me).

DEAR DR. BLONZ: Can niacin be harmful to one's health? I get some pretty bad rashes when I take niacin, and it seems like an allergic reaction. What do you say? -- N.L., Tucson, Arizona

DEAR N.L.: It is doubtful that you are allergic to niacin, which is an essential nutrient. The daily value for niacin on food labels is 20 milligrams per day. What you are probably experiencing is a "niacin flush," which is nothing more than a dilation of the small blood vessels near the skin. This can occur when a higher dose of the nutrient is taken, usually about 10 times the daily value. It varies from person to person; some can experience a flush at much lower doses.

A flush can be avoided by lowering your intake of niacin, taking it in divided doses or shifting to a "flush-free" form of niacin such as nicotinamide or inositol hexanicotinate.

Niacin -- also known as vitamin B3, or the related compounds nicotinic acid and nicotinamide -- is required for normal cell metabolism and energy release from carbohydrates. Niacin also plays a role in the synthesis of hormones and DNA. Food sources include organ meats, poultry, seafood, nuts, green vegetables and legumes. Some individuals take high levels of niacin to treat elevated cholesterol, but that may be less effective than was once thought. Read an update at tinyurl.com/nsa7ymn.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 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: Because they tend to be available year-round, carrots and broccoli are the staple vegetables in my diet. I select carrots with the tops attached to ensure reasonable freshness. My question is: How long can these two vegetables be kept in the refrigerator without losing a significant amount of their nutrients? -- D.D., Concord, California

DEAR D.D.: You have chosen a great pair of staples, ones that are available in most farmer's markets and food stores throughout the country. Depending on the way they are kept, you have a week or two with both.

Carrots can lose sweetness as they sit; purchasing carrots with greens intact provides a good indicator of just-picked freshness, as you say. Once purchased, though, you should remove the tops, as the greens tend to drain water and nutrients from the carrot. This makes perfect sense once you realize that the carrot is the root, i.e., the nutrient supplier, for the growing carrot plant.

Carrots store well in a refrigerator set no higher than 40 degrees F. They should be keep in a sealed plastic bag or container. They are at their nutrient and flavor peak for the first few days, and then begin to lose crispness and nutritional quality, slowly for the first couple of weeks, but then more quickly until they become limp.

Most of the carrots we get in the store are immature, having been picked that way to maximize tenderness and flavor. More mature carrots have a more "woody" texture and might not taste as sweet, but they can be kept for longer periods of time. In pre-refrigerator days, root crops such as carrots were kept in root cellars for up to six months. In those days, standalone taste was not as primary a consideration, as the vegetables were often used as ingredients in flavorful stews.

Broccoli, similar to carrots, keeps best at low temperatures (35 to 37 degrees F) in a high-humidity crisper drawer in the refrigerator. It can keep up to two weeks, and nutrient quality will slowly decrease during that time.

Temperature is the key. At temperatures just above freezing (32 degrees F), broccoli can be kept up to four weeks. This drops to two weeks if the temperature is 40 degrees F, and only five days if the temperature is 50 degrees F. Throughout all these storage periods, the nutrient content will slowly decrease. The University of Nebraska provides a good information page on the handling and storage of fruits and vegetables: tinyurl.com/mmgsvrw.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 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 am trying to get some answers about RNA and DNA, the nucleic acids. I have been reading information online, looking at products and reading a book that encourages you to take these substances as dietary supplements to help keep your body healthy and prevent aging-related chronic illnesses. Do you have information on this subject? Are these supplements safe to take, and are there any side effects? Do you know where to buy them? -- S.M., Phoenix

DEAR S.M.: Let's start with the bottom line: There is no reliable evidence that taking these compounds as dietary supplements will be a boon to your health, or provide any of the benefits you mention. Irrespective of that straightforward statement, there are plenty of products out there being touted for anti-aging and related benefits. For some background, let's take a closer look at the nucleic acids.

The principle nucleic acids are DNA (deoxyribonucleic acid), which is found mainly in the nucleus of our cells, and RNA (ribonucleic acid), which can be found throughout the cells. Both DNA and RNA are large, complex biochemical compounds that contain particular sequences of substances known as purine and pyrimidine bases. Similar to how sentences in Morse code are made up of dots and dashes, the arrangement of these bases in the nucleic acids contain a message, which, in this case, is the genetic blueprint of how we are made.

There was some thought, a number of years back, that increasing one's intake of nucleic acids would help slow down the aging process and ailments connected with getting older. There was even a popular book that came out in 1976 titled "Dr. Frank's No-Aging Diet" (by Benjamin S. Frank, Dial Press), in which the author put forth the concept that a decreasing level of the nucleic acids was one of the hallmarks of aging. The "logic" then suggested that by eating foods high in nucleic acids, or taking supplements of these compounds, you could "de-age" the body. Wouldn't it be nice if things were that simple?

Although it was characterized in the book as a "revolution in the making," there are a couple of problems with the logic. First, everyone's nucleic acids are unique. Most supplements of nucleic acids come from yeast, and it is a bit of a stretch to think that they would affect us as advertised. Another problem is that when consumed, the nucleic acids will be disassembled by the digestive system. Finally, individuals at risk for gout should be aware that taking nucleic acids increases your dietary intake of uric acid. All this being said, you can still find these dietary supplements at just about every online store.

Perhaps the most telling fact is that in the 38 years since the book was written, there has been little -- if any -- objective evidence to support the claims that taking nucleic acid supplements does anything more than provide profits to the marketers. This lack of evidence persists even now, when there are so many significant research efforts directed toward understanding the aging process.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 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.