DEAR DR. BLONZ: I recently had a blackout when I stood up after dinner. It is doubtful that it could be from dehydration, as I was drinking at the meal. Perhaps not enough salt?

I was working in the garden before dinner, and had been getting dizzy when I got up from sitting earlier in the day. Then after the meal, I stood for a minute and next thing I knew, I was on the floor. I think I was only out for a few seconds. I am active, often biking and running, and have had problems with heat exhaustion in the past. Any help/thoughts? -- S.T., Waukesha, Wisconsin

DEAR S.T.: There can be many explanations for an unexpected loss of consciousness; you have mentioned a few. It could have been a freak intersection of factors that ended up leading to a rapid drop in blood pressure (vasovagal episode). Staying hydrated is important, and if you tend to perspire heavily, it is reasonable to replenish lost electrolytes along with fluids when exercising or doing physical work. Anemia is also a possibility.

But -- and this is key -- I am not a physician and I have no real handle on other health issues in your life. You asked for my advice, so here it is: Make note of all the circumstances and share them with your health provider at your next opportunity. If anything like this has happened in the past, make the appointment now. If this type of weakness, dizziness or lightheadedness occurs again, make an immediate phone call to be seen and checked out by your physician. This may be nothing, but why take a chance?

DEAR DR. BLONZ: I buy special milk in bulk, usually a six-carton case at a time. The cartons usually have an expiration date two to three weeks in the future. If I freeze a couple of cartons as soon as I bring them home, then open them after the date on the carton, are they safe to use, and for how long? I'm not concerned about the taste because I blend the milk with protein powder and fresh fruit. I usually finish a carton within five to six days. -- B.S., Sun City, Arizona

DEAR B.S.: Assuming that the packages are appropriate for freezing, and there is sufficient air space to allow for normal expansion during the freezing process, I see no problem here from a food-safety standpoint. The clock stops during freezing. Any days left before the expiration date at the time of freezing transfer over to the time after the milk returns to its liquid state.

Also, blending the milk after it thaws, as you do, helps counter the fact that freezing tends to undo homogenization, meaning that milk fat tends to float on the surface in containers of defrosted milk. Even so, be sure to give the carton a good shake before pouring.

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: 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.