Skip to main content
Open Access Publications from the University of California


Excessive Vitamin A Consumption and Fractures: How Much is Too Much?

In 2001 the Food and Nutrition Board (FNB) of the Institute of Medicine, after reviewing the available literature, set the tolerable upper intake level of vitamin A at 3,000 g/day (1). While setting the upper intake level, the FNB chose not to factor into their decision several conflicting studies linking excessive vitamin A consumption with fractures. Since the vitamin A review, however, further studies have continued to solidify the relationship between high vitamin A intake and fracture risk. One such study found that ingestion of a daily amount of vitamin A significantly less than the tolerable upper intake level was associated with doubling the likelihood of a fracture (2). Many other studies like this one draw the same conclusions suggesting prudence in vitamin A consumption and the necessity of lowering the currently accepted tolerable upper intake level.

Plant Sterols and Stanols: An Additional Therapy for Cholesterol Management

Research has demonstrated that plant sterol and stanol ester-enriched margarine spreads lower LDL cholesterol by 9-14% (1). Maximal LDL reduction is achieved at plant sterol or stanol ester doses of 1.6-2.0 g/day (2,3). The mechanism for LDL reduction is the inhibition of cholesterol absorption in the gastrointestinal tract. For patients following a low-fat diet, plant sterols provide LDL-lowering beyond that obtained through diet alone. Plant sterols also provide additional LDL-lowering when used in conjunction with statins (2,4). Recent studies of esterified and non-esterified sterols and stanols in low-fat foods have demonstrated the same extent of LDL reduction observed with sterol ester-enriched fatty foods. Plant sterols and stanols appear safe, but are associated with decreased lycopene and carotene levels. However, these reductions can be prevented by consuming one additional serving/day of a high-carotenoid food (5). Despite demonstrated effectiveness and safety, sales of phytosterol-enriched products have been slow. Future research is needed to develop better marketing strategies and to expand the number of phytosterol-enriched products. The role of low levels of phytosterols present naturally in the diet should also be evaluated.

Controversies in Vitamin D Supplementation

Concurrent with the rise in vitamin D ingestion were the epidemic onsets of atherosclerosis and osteoporosis, which led to the hypothesis that vitamin D excess contributes to the development of these illnesses (1). A recent study found that vitamin D induced an increase in vascular smooth muscle cell migration in rat aorta, suggesting a possible mechanism of vitamin D in atherosclerosis (2). On the other hand, Rucker and colleagues found that 34% of the 188 healthy Canadians whom they tested were vitamin D insufficient in at least one occasion and recommended more aggressive vitamin D supplementation (3). Chapuy et al. reported that elderly women who took calcium and vitamin D supplements had reduced hip bone loss and risk of hip fracture (4). Although the research on vitamin D supplementation is still inconclusive, the potential association between high vitamin D ingestion and diseases such as atherosclerosis provides ample reason for caution. Since 15 minutes of exposure to sunlight three times a week is sufficient to produce the body's requirement of vitamin D, there is no need for healthy individuals to take vitamin D supplements (5). In addition, the current practice of rampant fortification of foods with vitamin D should be reevaluated.

Red Yeast Rice: An Easy Way to Lower Cholesterol

Hypercholesterolemia, a risk factor for atherosclerosis and associated cardiovascular diseases is currently widely treated with statins, potent inhibitors of HMO-CoA reductase the rate-limiting enzyme in cholesterol synthesis. Despite the proven benefits on the prevention of heart disease, the high cost of statin treatment, in addition to side effects on liver function resulted in the search for a more natural therapy. The finding was Cholestin, a red yeast rice dietary supplement prepared from rice fermented with red yeast (Monascus purpureus). Dating back to 800 AD during the Tang Dynasty in China this fermentation product has been used to make rice wine, maintain food color and taste, and serve as a medicine. Studies show that red yeast rice preparations significantly decrease total cholesterol levels in hyperlipidemic subjects (11). However, despite its promise as an alternative to conventional statin therapy, as a dietary supplement it is not restricted to standardized manufacturing guidelines and the contents of preparations vary widely between manufacturers. As a result, the beneficial findings found by some studies with Cholestin may not apply to the preparations available in stores. Thus, the full potential of Chinese red yeast rice will not be realized until standards of production and labeling are established (7).

Debunking the Effects of Taurine in Red Bull Energy Drink

Red Bull is a carbonated beverage that initially gained wide popularity in the U.S. during the late nineties. Taking root amongst college campuses, it appeared throughout underground clubs and eventually entered mainstream pop-culture. The manufactures claim that drinking Red Bull enhances physical endurance, concentration and reaction speed (1,6). The main ingredients of Red Bull include sugar, taurine, glucuronolactone and caffeine. It is hypothesized that the combinatorial influences of these ingredients are responsible for Red Bull’s proposed effects (9,10). This report critically reviews these claims and concludes that caffeine alone may be responsible for the proposed effects.

Acrylamide and Fried Foods: Should We Freak Out?

In April of 2002, the Swedish National Food Administration conducted a study where they found significant levels of the chemical acrylamide in fried foods such as potatoes and breakfast cereals [2]. Acrylamide forms at temperatures above 350o F (180o C) when the amino acid asparagine reacts with starch or sugars via Maillard reaction [6,7]. Although this chemical has been shown to be carcinogenic in rats [4], a study could not correlate any increase in risk of bowel, kidney or bladder cancer with the heavy intake of these fried foods containing acrylamide [10]. A possible explanation for this lack of correlation is that acrylamide is not present in sufficient quantities in these foods to cause appreciable toxicity or oncogenicity.