Carotenoids

Scientific studies (review articles) on the relationship between carotenoids and disease prevention:
One swallow does not make a summer. A famous Dutch saying that could not be any more obvious. Just because one single scientific study about a certain topic makes certain claims, it does not necessarily mean it is true. On the other hand, a review article (a collection of scientific studies on a certain topic) of randomized, placebo-controlled double blind clinical trials (RCTs) will answer the following question:
"Do taking dietary supplements make sense?" Yes for a positive conclusion and no for a negative conclusion.

One swallow does not make a summer. A famous Dutch saying that could not be any more obvious. Just because one single scientific study about a certain topic makes certain claims, it does not necessarily mean it is true. On the other hand, a review article (a collection of scientific studies on a certain topic) of cohort studies or case-control studies will answer the following question:
"Should I change my diet?".

1. Higher carotenoids levels reduce breast cancer
2. 25 mg carotenoid supplements decrease blood pressure 
3. Unsaturated fatty acids improve absorption of carotenoids
4. Higher concentrations of carotenoids reduce type 2 diabetes
5. Insufficiency of serum carotenoids increases overweight and obesity
6. 0.5-50 mg/d carotenoid supplementation improves cognitive performance among healthy adults
7. A high dietary intake of β-cryptoxanthin reduce osteoporosis and hip fracture
8. Carotenoid supplements decrease inflammation
9. >12 mg/day astaxanthin consumption causally reduce CRP levels
10. Higher circulating concentration of vitamin C, vitamin E and β-carotene reduce cardiovascular mortality
11. Higher concentration of carotenoids and vitamin E in blood reduce age-related macular degeneration
12. Dietary intake of 5 mg/d vitamin A reduces age-related cataract
13. Carotenoids may reduce risk of metabolic syndrome
14. A diet with high antioxidant properties reduces all-cause mortality risk
15. No association between vitamin A, C, D, E and lycopene and risk of non-Hodgkin lymphoma
16. Circulating concentrations of α-carotene, β-carotene and lutein and zeaxanthin reduce bladder cancer
17. Vitamin and antioxidant supplements have no overall preventive effect against bladder cancer
18. High β-carotene concentration reduces bladder cancer
19. High β-carotene dietary intake reduces Parkinson's disease among women
20. Higher concentration of carotenoids and vitamin E in blood reduce age-related macular degeneration
21. 300 μg/d dietary lutein and zeaxanthin intake reduce nuclear cataract
22. Higher lycopene exposure reduces risk of cardiovascular diseases
23. Daily 2 mg dietary lycopene consumption reduces prostate cancer risk
24. Tomatoes reduce cardiovascular risk among adults
25. Dietary intakes of vitamin C and E lower risk of Alzheimer's disease
26. Lower blood carotenoid level is a risk factor for dementia

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• More than 600 carotenoid compounds have been characterized.
  50 of these are consumed in the human diet.
  Approximately 12 carotenoids account for most of the dietary intake and they are found in measurable concentrations in human blood and tissues.
  The most common are lycopene, lutein, beta-carotene, alpha-carotene, beta-cryptoxanthin and zeaxanthine.
• Fewer than 10% of carotenoid serve as precursors of vitamin A.
  Beta-carotene, alpha-carotene and beta-cryptoxanthin have provitamin A activity.
  Lutein, lycopene and zeaxanthin cannot be converted to retinol, so they have no vitamin A activity.
• The vitamin A activity of beta-carotene in foods is 1/12 that of retinol (preformed vitamin A), while the vitamin A activities of alpha-carotene and beta-cryptoxanthin are both 1/24 that of retinol.
  1 RAE = 1 µg retinol (vitamin A).
  1 RAE = 2 µg all-trans-β-carotene as a supplement.
• An excess intake of carotenoids does not result in the production of excess quantities of vitamin A to cause intoxication.
• Green leafy vegetables and many colored fruits are rich in carotenoids.
  Lutein, zeaxanthin and canthaxanthin are present predominantly in green leafy vegetables and in fruit.
  Tomatoes and tomato-based food products are the major source of lycopene.
  The color of beta-carotene is masked by chlorophyll in green leafy vegetables.
• A good way to obtain sufficient amounts of carotenoids is 200-300 grams of vegetables and 2-5 servings of fruits per day.
• Carotenoids appear to be absorbed by duodenal mucosal cells by a mechanism involving passive diffusion, similar to that of cholesterol and the products of triglyceride lipolysis.
• Many carotenoids are absorbed better in the presence of dietary fats and from heat processed foods than from unprocessed sources.
• Trans-isomers of lycopene are absorbed more poorly than are cis-isomers.
• The amount of dietary fat required to ensure carotenoid absorption is 3-5 g per meal.
• Absorption efficiency of beta-carotene is estimated to be between 9-22%.
• Carotenoids may protect cells from oxidative stress by quenching free radicals capable of causing cellular damage.
• In well-nourished humans, carotenoids are present primarily in the adipose tissue (80-85%), liver (8-12%) and muscle (2-3%), with smaller amounts in other tissues.
• Of the total body pool of carotenoids (100-150 mg) in a well-nourished person, the serum usually contains approximately 1% and normally shows a concentration of 0.4-1.5 mcg/ml (0.8-8 micromol/l).
• Natural beta-carotene consists of two isomers; that is, two different structures of the same molecule. One is the all-trans and the other is the 9-cis; each contains the same a
• toms but in different arrangements.
  However, synthetic beta-carotene consists of only the all-trans form. The all-trans is converted to vitamin A much more efficiently than the 9-cis form.
• The EFSA (European Food Safety Authority) concludes that exposure to β-carotene from its use as food additive and as food supplement at a level below 15 mg/day do not give rise to concerns about adverse health effects in the general population, including heavy smokers.
• Carotenoids are E-numbers in the food industry, often used as food colorings.