In 1982, the famous monograph Diet, Nutrition and Cancer published by the US National Research Council reviewed this overwhelming
literature. It concluded “the epidemiological evidence is sufficient to suggest that foods rich in carotenes or Vitamin A are associated with a reduced risk of cancer.” The study recommended a diet including beta carotene rich vegetables to reduce cancer risks

A 1987 Israeli study demonstrated natural beta carotene is more effective than synthetic. Natural beta carotene is better assimilated by the body because it contains the 9-cis carotenoid isomer, lacking in synthetic carotene molecules. This means beta carotene in algae and vegetables greater antioxidant power than synthetic beta carotene. Controversy arose in 1995 when synthetic beta carotene was found ineffective preventing cancer in Finnish and U.S. smokers, and could even be harmful. Yet, these studies were flawed. Researchers chose only synthetic beta carotene lacking the cis isomer and gave high megadoses which may have caused nutrient imbalance. These studies reinforced the interest in natural carotenoids in whole foods.

Anti-cancer tumor effects

Because it is the richest natural beta carotene food, spirulina has been tested for anti-cancer effects. The Harvard University School of
Dental Medicine reduced oral cancer cells with spirulina extracts. A beta carotene solution applied to cancerous tumors in mouths of
hamsters reduced the number and size of tumors or caused them to disappear. When a beta carotene extract was fed to 20 hamsters
pretreated to develop mouth cancer, none developed the disease. Tissue samples contained an immune stimulating substance believed
to have destroyed cancer cells before they could multiply.

In 1995, spirulina reversed oral cancer in pan tobacco chewers in Kerala, India. Complete regression of oral leukoplakia was found in
45% of those using one gram a day for one year, compared to only 7% with a placebo. Within one year of discontinuing spirulina, 45%
of the lesions returned. This was the first human study of its chemopreventive potential.

Evidence linking natural beta carotene and cancer prevention is impressive. For those who do not eat 4-9 servings of fruits and vegetables daily, spirulina will add natural carotene insurance.