23 Nov 2015

The Institute of Cardiovascular Science and Medicine, The University of Hong Kong (HKU) hosted The 19^th Annual Scientific Meeting of The Institute of Cardiovascular Science and Medicine, in conjunction with the 10^th Across the Strait Scientific Conference on Cardiovascular Science on November 21. Experts from China, Hong Kong as well as Taiwan discussed important issues regarding to cardiovascular science and medicine during this conference. Experts and professors of Li Ka Shing Faculty of Medicine highlighted results of (I) Blood lead level and (II) Clinical Trial on Phytosterol during this conference.

I. Background of analysing blood lead level in the US population

Lead affects development in children but is also related to high blood pressure and kidney disease in adults. In Hong Kong, blood lead has been measured in specific groups but not systematically in the general population. In the United States, lead has been a public health concern for many years, so blood lead level in the general population is monitored nationally and reliable data have been collected.

Implications of gradual decline in blood lead levels in the US population

Research team led by Professor Bernard Cheung Man-yung, Sun Chieh Yeh Heart Foundation Professor in Cardiovascular Therapeutics, Clinical Professor of Department of Medicine, Li Ka Shing Faculty of Medicine, HKU analysed the data from the United States National Health and Nutrition Examination Survey (NHANES) from 1999 to 2012 and concluded gradual decline in blood lead level in the US population.¹ The average blood level in the US adults has dropped from 1.77 µg/dL in 1999-2000 to 1.09 µg/dL in 2011-2012. The average blood level in the US children and adolescents has dropped from 1.43 µg/dL in 1999-2000 to 0.66 µg/dL in 2011-2012. The proportion of children aged 1-5 with an elevated blood level (5 µg/dL or above) has dropped from 9.9% in 1999-2000 to 2.0% in 2011-2012.

The current blood lead reference level (5 µg/dL) was set in January 2012 with reference to the 2.5% of children aged 1-5 with the highest blood levels in NHANES 2007-2010.^2,3 However, with the continuous decrease in lead level, a new lower reference level is likely to be recommended in 2016. In Hong Kong, the reference level of 5 µg/dL, which was the same as the US reference level, was chosen after consultation with experts. Professor Cheung said that change in the US reference level may shed light on the situation in Hong Kong. However, it is too early to say if Hong Kong might follow the US when their new reference level is due to be announced in 2016.

Harmful effect of lead on human body

Lead is not needed by the body and there is no evidence of any beneficial effect on health. High blood lead level is associated with decreased IQ in children.⁴ Even at low blood lead levels, further decrease in the blood level is associated with higher IQ. In adults, blood lead level is weakly associated with hypertension, which might be due to its harmful effect on the kidneys.⁵ The best way to lower blood lead level is to reduce the amount of lead that gets into the body. An adequate intake of iron and calcium is also recommended. Unless the blood lead level is very high, chelation therapy is likely to do more harm than good. Chelation therapy is the medical procedure that involves the administration of chelating agents to remove heavy metals from the body. This administration can be oral, intravenous or intramuscular administration. Side effects of chelation therapy include allergy, hypocalcemia (low blood calcium level) etc.⁶

About the research team

This study was headed by Professor Bernard Cheung Man-yung, Sun Chieh Yeh Heart Foundation Professor in Cardiovascular Therapeutics, Clinical Professor of Department of Medicine, Li Ka Shing Faculty of Medicine, and Director of The Institute of Cardiovascular Science and Medicine of HKU, and Dr Tommy Cheung Tsang, Clinical Assistant Professor of the Department of Medicine, Li Ka Shing Faculty of Medicine, HKU.

II. Phytosterol: Natrual ingradient to reduce “bad cholesterol”

Cholesterol is one of the main risk factors for coronary heart disease, which is one of the top 3 causes of death in Hong Kong. Half of the people older than 45 years of age have high cholesterol. Every year, high cholesterol causes 2.6 million deaths in the world.⁷ Professor Bernard Cheung from the Department of Medicine and Dr Cheung Ching-lung from the Department of Pharmacology and Pharmacy at Li Ka Shing Faculty of Medicine, HKU conducted the first clinical trial on milk powders in Hong Kong people in July to August 2015. The primary objective of this study was to evaluate whether phytosterol, a natural ingredient, could lower cholesterol effectively.

Phytosterol is found in plants. This ingredient reduces absorption of cholesterol in the small intestines and lowers LDL, the “bad” cholesterol in blood. The European Food Safety Authority suggested daily intake of 1.5-2.4g of phytosterol,⁸ which is unlikely to be fulfilled eating a normal diet. Studies demonstrated a reduction of 7-10% in LDL cholesterol by taking 1.5-2.4g phytosterol daily for 2 to 3 weeks. Long term intake of phytosterol has a sustained effect on the LDL cholesterol level, especially in conjunction with a low fat diet and sufficient exercise. Every reduction of 0.6mmol/L cholesterol is associated with approximately 50% reduction in the risk of coronary heart disease.⁹ Therefore, people with elevated cholesterol level should pay attention to their cholesterol level promptly.

Results of the clinical trial

This study was conducted by the Department of Medicine and the Department of Pharmacology and Pharmacy. More than 200 participants with an average age of 53 took part in this study to evaluate whether phyosterol could reduce LDL cholesterol levels. Participants were required to drink milk made from a phytosterol-enriched milk powder twice a day; this gave a daily intake of 1.5g phytosterol. This amount of phytosterol is equivalent to the phytosterol contained in 132 cherries or 45 apples.¹⁰ During the press conference, Professor Bernard Cheung and Dr Cheung Ching-lung explained the effects of lipid profile and high blood cholesterol on cardiovascular disease, the effect of phytosterol on lipid profile as well as details of the study. In this randomised controlled trial, 110 and 111 participants took phytosterol-enriched high-calcium low-fat milk, or high-calcium low-fat milk without phytosterol respectively. Daily consumption of 1.5g phytosterol was associated with an average reduction of 9.46% in LDL cholesterol (p<0.0001) and an average reduction of 5.64% in total cholesterol (p<0.0001). Moreover, in study subjects who had elevated LDL cholesterol, there was a greater reduction in LDL cholesterol (-11.8%; p=0.01). In conclusion, our study proved that phytosterol-enriched milk lowers the LDL cholesterol level in the general population, and especially in people with elevated LDL cholesterol level. The key message of this study is that a natural substance can lower the cholesterol level.

About Phytosterol

Phytosterol is natural and safe. Most plants contain phytosterol, especially beans and nuts. It is suitable for different people, including those with normal cholesterol level, except children under 5, pregnant or lactating women. Phytosterol does not interfere with drugs that lower cholesterol; it can be taken concurrently. However, patients with heart disease, diabetes mellitus or very high cholesterol should consult their doctors for advice and should not rely only on phytosterol to reduce their cholesterol level.

About the research team

This study was headed by Professor Bernard Cheung Man-yung, Sun Chieh Yeh Heart Foundation Professor in Cardiovascular Therapeutics, Clinical Professor of Department of Medicine, Li Ka Shing Faculty of Medicine, and Director of The Institute of Cardiovascular Science and Medicine, HKU and Dr Cheung Ching-lung, Assistant Professor of the Department of Pharmacology and Pharmacy, Li Ka Shing Faculty of Medicine, HKU.

References

1. Tsoi MF, Cheung AJ, Cheung TT, et al. Fall in Blood Lead Level in the US Population 1999-2012. Journal of Hong Kong College of Cardiology 2015;23:122.
2. Centers for Disease Control and Prevention's Advisory Committee for Childhood Lead Poisoning Prevention. CDC Response to Advisory Committee on Childhood Lead Poisoning Prevention Recommendations in "Low Level Lead Exposure Harms Children: A Renewed Call of Primary Prevention". Secondary CDC Response to Advisory Committee on Childhood Lead Poisoning Prevention Recommendations in "Low Level Lead Exposure Harms Children: A Renewed Call of Primary Prevention" 2012. http://www.cdc.gov/nceh/lead/acclpp/cdc_response_lead_exposure_recs.pdf.
3. Wheeler W, Brown MJ. Blood Lead Levels in Children Aged 1-5 Years - United States, 1999-2010. MMWR 2013;62(13):245-48.
4. Canfield RL, Henderson CR, Cory-Slechta DA, et al. Intellectual Impairment in Children with Blood Lead Concentrations below 10 µg per Deciliter. New England Journal of Medicine 2003;348(16):1517-26.
5. Patrick L. Lead Toxicity, A Review of the Literature. Part I: Exposure, Evaluation, and Treatment. Alternative Medicine Review 2006;11(1):2-22.
6. Rogen WJ, Dietrich KN, Ware JH, et al. The Effect of Chelation Therapy with Succimer on Neuropsychological Development in Children Exposed to Lead. New England Journal of Medicine 2001;344(19):1421-26.
7. Centre for Health Protection, HK. 智對膽固醇. Available at http://www.chp.gov.hk/files/pdf/ncd_watch_sep2011_chi.pdf
8. Micalef MA, Garg ML. The lipid-lowering effects of phytosterols and (n-3) polyunsaturated fatty adds are synergistic and complementary in hyperlipidemic men and women. J Nutr 2008:138:1086-1090
9. Law MR, Wald NJ, Thompson SG. By how much and how quickly does reduction in serum cholesterol concentration lower risk of ischemic heart diseases? Bmju 1994:308:367-372.
10. Weihrauch JL, Gardner JM, Sterol content of foods of plant origin. J Am Diet Assoc 1978:73:39- 47

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